1.
Using Split-Apply-Combine for Data Analysis in
Clojure
Bay Area Clojure Group
June 6, 2013
Tom Faulhaber
twitter: @tomfaulhaber
github: tomfaulhaber
Saturday, June 8, 13

2.
Saturday, June 8, 13

3.
Saturday, June 8, 13

4.
Saturday, June 8, 13

5.
Saturday, June 8, 13

6.
Saturday, June 8, 13

7.
Data Structures for Data
Analysis
Saturday, June 8, 13

8.
The Vector
[265.0 259.98 266.89 262.22 ...]
Saturday, June 8, 13

9.
The Vector
(mean [265.0 259.98 266.89 262.22 ...])
➜
263.697
Saturday, June 8, 13

10.
The Vector
(apply min [265.0 259.98 266.89 262.22 ...])
➜
257.21
Saturday, June 8, 13

11.
The Vector
(apply max [265.0 259.98 266.89 262.22 ...])
➜
269.75
Saturday, June 8, 13

12.
The Vector
(sd [265.0 259.98 266.89 262.22 ...])
➜
3.815
Saturday, June 8, 13

13.
The Vector
(quantile [265.0 259.98 266.89 262.22 ...])
➜
[257.21 260.105 264.27 266.175 269.75]
Saturday, June 8, 13

14.
The Vector
[265.0 259.98 266.89 262.22 ...]
Saturday, June 8, 13

15.
The Vector
(histogram [265.0 259.98 266.89 262.22 ...])
➜
Saturday, June 8, 13

16.
The Vector
[265.0 259.98 266.89 262.22 ...]
Saturday, June 8, 13

17.
The Vector
(line-chart [265.0 259.98 266.89 262.22 ...])
➜
Saturday, June 8, 13

18.
The Matrix
Saturday, June 8, 13

19.
The Matrix
1 Dimension
0
1
2
3
4
5
6
0 1 2 3 4
Saturday, June 8, 13

20.
The Matrix
1 Dimension
0
1
2
3
4
5
6
0 1 2 3 4
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
2 Dimensions
Saturday, June 8, 13

21.
The Matrix
1 Dimension
0
1
2
3
4
5
6
0 1 2 3 4
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
2 Dimensions
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
3 Dimensions
Saturday, June 8, 13

22.
Key-Value Pairs
{ "IBM" [205.18 203.79 202.79 201.02 ...],
"MSFT" [27.93 27.44 27.5 27.34 ...],
"AMZN" [265.0 259.98 266.89 262.22 ...]}
Using Key-Value pairs can organize multiple data
units (such as trials, customers, etc.) or collect
parameter data
Saturday, June 8, 13

23.
The Dataset
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
Saturday, June 8, 13

24.
The Dataset
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
Items in column have same type
Saturday, June 8, 13

25.
The Dataset
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
Across a row, there may be different types
Saturday, June 8, 13

26.
The Dataset
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
Saturday, June 8, 13

27.
The Dataset
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
Identifiers
Saturday, June 8, 13

28.
The Dataset
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
Identifiers Measurements
Saturday, June 8, 13

29.
Split-Apply-Combine
Saturday, June 8, 13

30.
Split-Apply-Combine
Pattern described by Hadley
Wickham and implemented in the
plyr library for R.
Home page: http://plyr.had.co.nz
JSS Journal of Statistical Software
April 2011, Volume 40, Issue 1. http://www.jstatsoft.org/
The Split-Apply-Combine Strategy for Data
Analysis
Hadley Wickham
Rice University
Abstract
Many data analysis problems involve the application of a split-apply-combine strategy,
where you break up a big problem into manageable pieces, operate on each piece inde-
pendently and then put all the pieces back together. This insight gives rise to a new R
package that allows you to smoothly apply this strategy, without having to worry about
the type of structure in which your data is stored.
The paper includes two case studies showing how these insights make it easier to work
with batting records for veteran baseball players and a large 3d array of spatio-temporal
ozone measurements.
Keywords: R, apply, split, data analysis.
1. Introduction
What do we do when we analyze data? What are common actions and what are common
mistakes? Given the importance of this activity in statistics, there is remarkably little research
on how data analysis happens. This paper attempts to remedy a very small part of that lack by
describing one common data analysis pattern: Split-apply-combine. You see the split-apply-
combine strategy whenever you break up a big problem into manageable pieces, operate on
each piece independently and then put all the pieces back together. This crops up in all stages
of an analysis:
During data preparation, when performing group-wise ranking, standardization, or nor-
malization, or in general when creating new variables that are most easily calculated on
a per-group basis.
When creating summaries for display or analysis, for example, when calculating marginal
means, or conditioning a table of counts by dividing out group sums.
Saturday, June 8, 13

31.
Split
Apply
Combine
Saturday, June 8, 13

32.
Split
Apply
Combine
the object based on dimension(s) or identifiers
(yielding segments of the same type)
Saturday, June 8, 13

33.
Split
Apply
Combine
the object based on dimension(s) or identifiers
(yielding segments of the same type)
a function to each segment producing a new segment of
the target type. The function can aggregate or transform
the segment.
Saturday, June 8, 13

34.
Split
Apply
Combine
the object based on dimension(s) or identifiers
(yielding segments of the same type)
a function to each segment producing a new segment of
the target type. The function can aggregate or transform
the segment.
the results into an output type (possibly of higher
dimension)
Saturday, June 8, 13

35.
Variations based on interface
Output
Input
Array Data.Frame List Discarded
Array
Data.Frame
List
aaply adply alply a_ply
daply ddply dlply d_ply
laply ldply llply l_ply
From: Wickham, The Split-Apply-Combine Strategy for Data Analysis
Saturday, June 8, 13

36.
Splitting Matrices - 2D
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
Split each element to a
scalar
Saturday, June 8, 13

37.
Splitting Matrices - 2D
Split each column to a
vector
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
Saturday, June 8, 13

38.
Splitting Matrices - 2D
Split each row to a vector
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
Saturday, June 8, 13

39.
Splitting Matrices - 2D
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
Split each element to a
scalar
Split each column to a
vector
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
Split each row to a vector
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
Saturday, June 8, 13

40.
Splitting Matrices - 3D
0 1 2 3 4 5 6 7
1
2
3
4
5
6
1
2
3
0
0
Split each element to a
scalar
Saturday, June 8, 13

41.
Splitting Matrices - 3D
1 2 3 4 5 6 7
0
1
2
3
0
0
1
2
3
4
5
6
Split each row x=c1, y=c2 to
a vector
Saturday, June 8, 13

42.
Splitting Matrices - 3D
Split each row x=c1, z=c2 to
a vector
0 1 2 3 4 5 6 7
1
2
3
4
5
6
0
0
1
2
3
Saturday, June 8, 13

43.
Splitting Matrices - 3D
0 1 2 3 4 5 6 7
1
2
3
4
5
6
1
2
3
0
0
Split each row y=c1, z=c2 to
a vector
Saturday, June 8, 13

44.
Splitting Matrices - 3D
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
Split each slice x=c to a 2D
matrix
Saturday, June 8, 13

45.
Splitting Matrices - 3D
Split each slice y=c to a 2D
matrix
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
Saturday, June 8, 13

46.
Splitting Matrices - 3D
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
Split each slice z=c to a 2D
matrix
Saturday, June 8, 13

47.
Splitting Matrices - 3D
0 1 2 3 4 5 6 7
1
2
3
4
5
6
1
2
3
0
0
Split each element to a scalar
1 2 3 4 5 6 7
0
1
2
3
0
0
1
2
3
4
5
6
Split each row x=c1, y=c2 to a vector
Split each row x=c1, z=c2 to a vector
0 1 2 3 4 5 6 7
1
2
3
4
5
6
0
0
1
2
3
0 1 2 3 4 5 6 7
1
2
3
4
5
6
1
2
3
0
0
Split each row y=c1, z=c2 to a vector
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
Split each slice x=c to a 2D matrix
Split each slice y=c to a 2D matrix
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
0 1 2 3 4 5 6 7
0
1
2
3
4
5
6
0
1
2
3
Split each slice z=c to a 2D matrix
Saturday, June 8, 13

48.
Splitting a Dataset
Split by Symbol
2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
...
2013-02-05
Date
2013-02-04
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
AMZN 259.98264.68 259.98 3723600259.07262.78
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
2013-02-01
Date
2013-02-04 203.57205.02 201.99IBM 204.19 3188800203.79
204.65 203.37IBM 203.84 3370700205.35 205.18
Adj CloseVolumeCloseLowHighOpenSymbol
Date
2013-02-04
2013-02-01
MSFT 27.4427.87 50540000 27.0328.02 27.42
27.93 27.51MSFT 28.05 5556590027.5527.67
Adj CloseVolumeCloseLowHighOpenSymbol
Saturday, June 8, 13

49.
Splitting a Dataset
Split by Date
... 2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
2013-02-01
Date
2013-02-01
2013-02-01 27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
Date
2013-02-04
2013-02-04
2013-02-04
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
Adj CloseVolumeCloseLowHighOpenSymbol
2013-02-05
Date
261.46 266.89268.03AMZN 4012900262.00 266.89
Adj CloseVolumeCloseLowHighOpenSymbol
Saturday, June 8, 13

50.
Splitting a Dataset
Split by Date
... 2013-02-05
2013-02-01
Date
2013-02-04
2013-02-04
2013-02-04
2013-02-01
2013-02-01
261.46 266.89268.03AMZN 4012900262.00 266.89
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
2013-02-01
Date
2013-02-01
2013-02-01 27.93 27.51MSFT 28.05 5556590027.5527.67
204.65 203.37IBM 203.84 3370700205.35 205.18
265.00268.93 6115000AMZN 268.93 262.80 265.00
Adj CloseVolumeCloseLowHighOpenSymbol
Date
2013-02-04
2013-02-04
2013-02-04
MSFT 27.4427.87 50540000 27.0328.02 27.42
203.57205.02 201.99IBM 204.19 3188800203.79
AMZN 259.98264.68 259.98 3723600259.07262.78
Adj CloseVolumeCloseLowHighOpenSymbol
2013-02-05
Date
261.46 266.89268.03AMZN 4012900262.00 266.89
Adj CloseVolumeCloseLowHighOpenSymbol
We’ll see more advanced splitting in the case study
Saturday, June 8, 13

51.
Apply
0
0
1
2
3
Saturday, June 8, 13

52.
Apply
(func )
0
0
1
2
3
Saturday, June 8, 13

53.
Apply
(func )
0
0
1
2
3
➜
result
Saturday, June 8, 13

54.
Apply
(func )
result must be appropriate for output type
0
0
1
2
3
➜
result
Saturday, June 8, 13

55.
Combine
Assemble apply results into output
5
4
3
2
1
0
0
1
2
3
5
4
3
2
1
0
0
1
2
3
Saturday, June 8, 13

56.
Implementing ddply in
Clojure
Saturday, June 8, 13

57.
Implementing ddply
(ns split-apply-combine.ply
"Implementation of the split-apply-combine functions, similar to R's plyr library."
(:use [incanter.core :only [$data col-names conj-rows dataset]])
(:require [split-apply-combine.core :as sac]))
(defn fast-conj-rows
"A simple version of conj-rows that runs much faster"
[& datasets]
(when (seq datasets)
(dataset (col-names (first datasets))
(mapcat :rows datasets))))
(defn expr-to-fn
[expr]
(let [row-param (gensym "row-")
kw-map (sac/build-keyword-map expr)]
`(fn [~row-param]
(let [~@(apply concat
(for [[kw sym] kw-map]
[sym `(get ~row-param ~kw ~kw)]))]
~(sac/convert-keywords expr kw-map)))))
(defn exprs-to-fns
[group-by]
(if (coll? group-by)
(vec (for [item group-by]
(if (and (coll? item)
(coll? (second item))
(not (#{'fn 'fn*} (first (second item)))))
[(first item) (expr-to-fn (second item))]
item)))
group-by))
(defn split-ds
"Perform a split operation on data, which must be a dataset, using the group-by-fns
to choose bins. group-by-fns can either be a single function or a collection of
functions. In the latter case, the results will be combined to create a key for
the bin. Returns a map of the group-by-fns results to datasets including all
the rows that had the given result.
Note that keyword column names are the most common functions to use for the
group-by."
[group-by-fns data]
(let [cols (col-names data)
group-by-fn (if (= 1 (count group-by-fns))
(first group-by-fns)
(apply juxt group-by-fns))]
(loop [cur (:rows data) row-groups {}]
(if (empty? cur)
(for [[group rows] row-groups] [group (dataset cols rows)])
(recur (next cur)
(let [row (first cur)
k (group-by-fn row)
a (row-groups k)]
(assoc row-groups k (if a (conj a row) [row]))))))))
(defn apply-ds
"Apply fun to each group in grouped-data returning a sequence of pairs of the
original group-keys and the result of applying the function the dataset. See
split-ds for information on the grouped-data data structure."
[fun grouped-data]
(for [[group split-data] grouped-data]
[group (fun split-data)]))
(defn combine-ds
"Combine the datasets in grouped-data into a single dataset including the
columns specified in the group-by argument as having the values found in
the keys in the grouped data.
If there are columns that are in both the key and the dataset, the values
in the key have precedence."
[group-by grouped-data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by-filter (complement (set group-by))]
(apply fast-conj-rows
(for [[group data] grouped-data]
(let [grouped-cols (zipmap group-by group)
union-cols (concat group-by
(filter group-by-filter
(col-names data)))]
(dataset union-cols
(map #(merge % grouped-cols)
(:rows data))))))))
(defn ddply*
"Split-apply-combine from datasets to datasets.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply* :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply* [[:Month #((juxt year month) (:timestamp %)]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(->> data
(split-ds (map second group-by))
(apply-ds fun)
(combine-ds (map first group-by))))))
(defmacro ddply
"Split-apply-combine from datasets to datasets. This macro is a wrapper on ddply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword key-expr] where the
exression key-expr is tranformed to a function and in expr are expanded to accessors
on rows. The resulting function is applied to each row to generate the key for
that row. When the groups are combined, keyword is used as the column name for
the resulting column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply [[:Month ((juxt year month) :timestamp]]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
`(ddply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(ddply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn d_ply*
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply* :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(dorun
(->> data
(split-ds (map second group-by))
(apply-ds fun))))))
(defmacro d_ply
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects. This macro is a wrapper on d_ply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
`(d_ply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(d_ply* ~(exprs-to-fns group-by) ~fun ~data)))
Saturday, June 8, 13

58.
Implementing ddply - Split
(ns split-apply-combine.ply
"Implementation of the split-apply-combine functions, similar to R's plyr library."
(:use [incanter.core :only [$data col-names conj-rows dataset]])
(:require [split-apply-combine.core :as sac]))
(defn fast-conj-rows
"A simple version of conj-rows that runs much faster"
[& datasets]
(when (seq datasets)
(dataset (col-names (first datasets))
(mapcat :rows datasets))))
(defn expr-to-fn
[expr]
(let [row-param (gensym "row-")
kw-map (sac/build-keyword-map expr)]
`(fn [~row-param]
(let [~@(apply concat
(for [[kw sym] kw-map]
[sym `(get ~row-param ~kw ~kw)]))]
~(sac/convert-keywords expr kw-map)))))
(defn exprs-to-fns
[group-by]
(if (coll? group-by)
(vec (for [item group-by]
(if (and (coll? item)
(coll? (second item))
(not (#{'fn 'fn*} (first (second item)))))
[(first item) (expr-to-fn (second item))]
item)))
group-by))
(defn split-ds
"Perform a split operation on data, which must be a dataset, using the group-by-fns
to choose bins. group-by-fns can either be a single function or a collection of
functions. In the latter case, the results will be combined to create a key for
the bin. Returns a map of the group-by-fns results to datasets including all
the rows that had the given result.
Note that keyword column names are the most common functions to use for the
group-by."
[group-by-fns data]
(let [cols (col-names data)
group-by-fn (if (= 1 (count group-by-fns))
(first group-by-fns)
(apply juxt group-by-fns))]
(loop [cur (:rows data) row-groups {}]
(if (empty? cur)
(for [[group rows] row-groups] [group (dataset cols rows)])
(recur (next cur)
(let [row (first cur)
k (group-by-fn row)
a (row-groups k)]
(assoc row-groups k (if a (conj a row) [row]))))))))
(defn apply-ds
"Apply fun to each group in grouped-data returning a sequence of pairs of the
original group-keys and the result of applying the function the dataset. See
split-ds for information on the grouped-data data structure."
[fun grouped-data]
(for [[group split-data] grouped-data]
[group (fun split-data)]))
(defn combine-ds
"Combine the datasets in grouped-data into a single dataset including the
columns specified in the group-by argument as having the values found in
the keys in the grouped data.
If there are columns that are in both the key and the dataset, the values
in the key have precedence."
[group-by grouped-data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by-filter (complement (set group-by))]
(apply fast-conj-rows
(for [[group data] grouped-data]
(let [grouped-cols (zipmap group-by group)
union-cols (concat group-by
(filter group-by-filter
(col-names data)))]
(dataset union-cols
(map #(merge % grouped-cols)
(:rows data))))))))
(defn ddply*
"Split-apply-combine from datasets to datasets.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply* :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply* [[:Month #((juxt year month) (:timestamp %)]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(->> data
(split-ds (map second group-by))
(apply-ds fun)
(combine-ds (map first group-by))))))
(defmacro ddply
"Split-apply-combine from datasets to datasets. This macro is a wrapper on ddply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword key-expr] where the
exression key-expr is tranformed to a function and in expr are expanded to accessors
on rows. The resulting function is applied to each row to generate the key for
that row. When the groups are combined, keyword is used as the column name for
the resulting column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply [[:Month ((juxt year month) :timestamp]]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
`(ddply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(ddply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn d_ply*
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply* :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(dorun
(->> data
(split-ds (map second group-by))
(apply-ds fun))))))
(defmacro d_ply
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects. This macro is a wrapper on d_ply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
`(d_ply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(d_ply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn split-ds
[group-by-fns data]
(let [cols (col-names data)
group-by-fn (if (= 1 (count group-by-fns))
(first group-by-fns)
(apply juxt group-by-fns))]
(loop [cur (:rows data) row-groups {}]
(if (empty? cur)
(for [[group rows] row-groups] [group (dataset cols rows)])
(recur (next cur)
(let [row (first cur)
k (group-by-fn row)
a (row-groups k)]
(assoc row-groups k (if a (conj a row) [row]))))))))
Saturday, June 8, 13

59.
Implementing ddply - Apply
(ns split-apply-combine.ply
"Implementation of the split-apply-combine functions, similar to R's plyr library."
(:use [incanter.core :only [$data col-names conj-rows dataset]])
(:require [split-apply-combine.core :as sac]))
(defn fast-conj-rows
"A simple version of conj-rows that runs much faster"
[& datasets]
(when (seq datasets)
(dataset (col-names (first datasets))
(mapcat :rows datasets))))
(defn expr-to-fn
[expr]
(let [row-param (gensym "row-")
kw-map (sac/build-keyword-map expr)]
`(fn [~row-param]
(let [~@(apply concat
(for [[kw sym] kw-map]
[sym `(get ~row-param ~kw ~kw)]))]
~(sac/convert-keywords expr kw-map)))))
(defn exprs-to-fns
[group-by]
(if (coll? group-by)
(vec (for [item group-by]
(if (and (coll? item)
(coll? (second item))
(not (#{'fn 'fn*} (first (second item)))))
[(first item) (expr-to-fn (second item))]
item)))
group-by))
(defn split-ds
"Perform a split operation on data, which must be a dataset, using the group-by-fns
to choose bins. group-by-fns can either be a single function or a collection of
functions. In the latter case, the results will be combined to create a key for
the bin. Returns a map of the group-by-fns results to datasets including all
the rows that had the given result.
Note that keyword column names are the most common functions to use for the
group-by."
[group-by-fns data]
(let [cols (col-names data)
group-by-fn (if (= 1 (count group-by-fns))
(first group-by-fns)
(apply juxt group-by-fns))]
(loop [cur (:rows data) row-groups {}]
(if (empty? cur)
(for [[group rows] row-groups] [group (dataset cols rows)])
(recur (next cur)
(let [row (first cur)
k (group-by-fn row)
a (row-groups k)]
(assoc row-groups k (if a (conj a row) [row]))))))))
(defn apply-ds
"Apply fun to each group in grouped-data returning a sequence of pairs of the
original group-keys and the result of applying the function the dataset. See
split-ds for information on the grouped-data data structure."
[fun grouped-data]
(for [[group split-data] grouped-data]
[group (fun split-data)]))
(defn combine-ds
"Combine the datasets in grouped-data into a single dataset including the
columns specified in the group-by argument as having the values found in
the keys in the grouped data.
If there are columns that are in both the key and the dataset, the values
in the key have precedence."
[group-by grouped-data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by-filter (complement (set group-by))]
(apply fast-conj-rows
(for [[group data] grouped-data]
(let [grouped-cols (zipmap group-by group)
union-cols (concat group-by
(filter group-by-filter
(col-names data)))]
(dataset union-cols
(map #(merge % grouped-cols)
(:rows data))))))))
(defn ddply*
"Split-apply-combine from datasets to datasets.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply* :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply* [[:Month #((juxt year month) (:timestamp %)]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(->> data
(split-ds (map second group-by))
(apply-ds fun)
(combine-ds (map first group-by))))))
(defmacro ddply
"Split-apply-combine from datasets to datasets. This macro is a wrapper on ddply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword key-expr] where the
exression key-expr is tranformed to a function and in expr are expanded to accessors
on rows. The resulting function is applied to each row to generate the key for
that row. When the groups are combined, keyword is used as the column name for
the resulting column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply [[:Month ((juxt year month) :timestamp]]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
`(ddply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(ddply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn d_ply*
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply* :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(dorun
(->> data
(split-ds (map second group-by))
(apply-ds fun))))))
(defmacro d_ply
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects. This macro is a wrapper on d_ply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
`(d_ply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(d_ply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn apply-ds
[fun grouped-data]
(for [[group split-data] grouped-data]
[group (fun split-data)]))
Saturday, June 8, 13

60.
Implementing ddply - Combine
(ns split-apply-combine.ply
"Implementation of the split-apply-combine functions, similar to R's plyr library."
(:use [incanter.core :only [$data col-names conj-rows dataset]])
(:require [split-apply-combine.core :as sac]))
(defn fast-conj-rows
"A simple version of conj-rows that runs much faster"
[& datasets]
(when (seq datasets)
(dataset (col-names (first datasets))
(mapcat :rows datasets))))
(defn expr-to-fn
[expr]
(let [row-param (gensym "row-")
kw-map (sac/build-keyword-map expr)]
`(fn [~row-param]
(let [~@(apply concat
(for [[kw sym] kw-map]
[sym `(get ~row-param ~kw ~kw)]))]
~(sac/convert-keywords expr kw-map)))))
(defn exprs-to-fns
[group-by]
(if (coll? group-by)
(vec (for [item group-by]
(if (and (coll? item)
(coll? (second item))
(not (#{'fn 'fn*} (first (second item)))))
[(first item) (expr-to-fn (second item))]
item)))
group-by))
(defn split-ds
"Perform a split operation on data, which must be a dataset, using the group-by-fns
to choose bins. group-by-fns can either be a single function or a collection of
functions. In the latter case, the results will be combined to create a key for
the bin. Returns a map of the group-by-fns results to datasets including all
the rows that had the given result.
Note that keyword column names are the most common functions to use for the
group-by."
[group-by-fns data]
(let [cols (col-names data)
group-by-fn (if (= 1 (count group-by-fns))
(first group-by-fns)
(apply juxt group-by-fns))]
(loop [cur (:rows data) row-groups {}]
(if (empty? cur)
(for [[group rows] row-groups] [group (dataset cols rows)])
(recur (next cur)
(let [row (first cur)
k (group-by-fn row)
a (row-groups k)]
(assoc row-groups k (if a (conj a row) [row]))))))))
(defn apply-ds
"Apply fun to each group in grouped-data returning a sequence of pairs of the
original group-keys and the result of applying the function the dataset. See
split-ds for information on the grouped-data data structure."
[fun grouped-data]
(for [[group split-data] grouped-data]
[group (fun split-data)]))
(defn combine-ds
"Combine the datasets in grouped-data into a single dataset including the
columns specified in the group-by argument as having the values found in
the keys in the grouped data.
If there are columns that are in both the key and the dataset, the values
in the key have precedence."
[group-by grouped-data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by-filter (complement (set group-by))]
(apply fast-conj-rows
(for [[group data] grouped-data]
(let [grouped-cols (zipmap group-by group)
union-cols (concat group-by
(filter group-by-filter
(col-names data)))]
(dataset union-cols
(map #(merge % grouped-cols)
(:rows data))))))))
(defn ddply*
"Split-apply-combine from datasets to datasets.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply* :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply* [[:Month #((juxt year month) (:timestamp %)]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(->> data
(split-ds (map second group-by))
(apply-ds fun)
(combine-ds (map first group-by))))))
(defmacro ddply
"Split-apply-combine from datasets to datasets. This macro is a wrapper on ddply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword key-expr] where the
exression key-expr is tranformed to a function and in expr are expanded to accessors
on rows. The resulting function is applied to each row to generate the key for
that row. When the groups are combined, keyword is used as the column name for
the resulting column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply [[:Month ((juxt year month) :timestamp]]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
`(ddply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(ddply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn d_ply*
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply* :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(dorun
(->> data
(split-ds (map second group-by))
(apply-ds fun))))))
(defmacro d_ply
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects. This macro is a wrapper on d_ply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
`(d_ply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(d_ply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn combine-ds
[group-by grouped-data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by-filter (complement (set group-by))]
(apply fast-conj-rows
(for [[group data] grouped-data]
(let [grouped-cols (zipmap group-by group)
union-cols (concat group-by
(filter group-by-filter
(col-names data)))]
(dataset union-cols
(map #(merge % grouped-cols)
(:rows data))))))))
Saturday, June 8, 13

61.
Implementing ddply - Putting it all together
(ns split-apply-combine.ply
"Implementation of the split-apply-combine functions, similar to R's plyr library."
(:use [incanter.core :only [$data col-names conj-rows dataset]])
(:require [split-apply-combine.core :as sac]))
(defn fast-conj-rows
"A simple version of conj-rows that runs much faster"
[& datasets]
(when (seq datasets)
(dataset (col-names (first datasets))
(mapcat :rows datasets))))
(defn expr-to-fn
[expr]
(let [row-param (gensym "row-")
kw-map (sac/build-keyword-map expr)]
`(fn [~row-param]
(let [~@(apply concat
(for [[kw sym] kw-map]
[sym `(get ~row-param ~kw ~kw)]))]
~(sac/convert-keywords expr kw-map)))))
(defn exprs-to-fns
[group-by]
(if (coll? group-by)
(vec (for [item group-by]
(if (and (coll? item)
(coll? (second item))
(not (#{'fn 'fn*} (first (second item)))))
[(first item) (expr-to-fn (second item))]
item)))
group-by))
(defn split-ds
"Perform a split operation on data, which must be a dataset, using the group-by-fns
to choose bins. group-by-fns can either be a single function or a collection of
functions. In the latter case, the results will be combined to create a key for
the bin. Returns a map of the group-by-fns results to datasets including all
the rows that had the given result.
Note that keyword column names are the most common functions to use for the
group-by."
[group-by-fns data]
(let [cols (col-names data)
group-by-fn (if (= 1 (count group-by-fns))
(first group-by-fns)
(apply juxt group-by-fns))]
(loop [cur (:rows data) row-groups {}]
(if (empty? cur)
(for [[group rows] row-groups] [group (dataset cols rows)])
(recur (next cur)
(let [row (first cur)
k (group-by-fn row)
a (row-groups k)]
(assoc row-groups k (if a (conj a row) [row]))))))))
(defn apply-ds
"Apply fun to each group in grouped-data returning a sequence of pairs of the
original group-keys and the result of applying the function the dataset. See
split-ds for information on the grouped-data data structure."
[fun grouped-data]
(for [[group split-data] grouped-data]
[group (fun split-data)]))
(defn combine-ds
"Combine the datasets in grouped-data into a single dataset including the
columns specified in the group-by argument as having the values found in
the keys in the grouped data.
If there are columns that are in both the key and the dataset, the values
in the key have precedence."
[group-by grouped-data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by-filter (complement (set group-by))]
(apply fast-conj-rows
(for [[group data] grouped-data]
(let [grouped-cols (zipmap group-by group)
union-cols (concat group-by
(filter group-by-filter
(col-names data)))]
(dataset union-cols
(map #(merge % grouped-cols)
(:rows data))))))))
(defn ddply*
"Split-apply-combine from datasets to datasets.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply* :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply* [[:Month #((juxt year month) (:timestamp %)]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(->> data
(split-ds (map second group-by))
(apply-ds fun)
(combine-ds (map first group-by))))))
(defmacro ddply
"Split-apply-combine from datasets to datasets. This macro is a wrapper on ddply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and combines the result of that
back into a single dataset.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword key-expr] where the
exression key-expr is tranformed to a function and in expr are expanded to accessors
on rows. The resulting function is applied to each row to generate the key for
that row. When the groups are combined, keyword is used as the column name for
the resulting column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Examples:
(ddply :Symbol
(transform :Change = (diff0 :Close))
stock-data)
(ddply [[:Month ((juxt year month) :timestamp]]]
(colwise :Volume sum)
stock-data)"
([group-by fun]
`(ddply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(ddply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn d_ply*
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply* :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(dorun
(->> data
(split-ds (map second group-by))
(apply-ds fun))))))
(defmacro d_ply
"Split-apply-combine from datasets to nothing. This version ignores the output of
fun and is used for fun's side effects. This macro is a wrapper on d_ply*
which provides translation of simple column-referencing expressions in the group-by
argument.
Splits data into a the group of datasets as specified by the group-by argument,
applies fun to each of the resulting datasets and then drops the result.
The group-by argument can be a keyword or collection of keywords which specify
the columns to group by. It can also include pairs [keyword keyfn] where the
function keyfun is applied to each row to generate the key for that row. When
the groups are combined, keyword is used as the column name for the resulting
column. The two types of group-by specifications can be mixed.
The result of the apply function can contain the same columns names as the
original dataset or different ones. It can contain the same number of rows as
the original, a different number, or a single row.
If data is not specified, it defaults to the currently bound value of $data.
Example:
(d_ply :Symbol
#(view (bar-chart :Date :Volume :data %))
stock-data)"
([group-by fun]
`(d_ply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(d_ply* ~(exprs-to-fns group-by) ~fun ~data)))
(defn ddply*
([group-by fun]
(ddply* group-by fun $data))
([group-by fun data]
(let [group-by (if (coll? group-by) group-by [group-by])
group-by (for [item group-by]
(if (coll? item) item [item item]))]
(->> data
(split-ds (map second group-by))
(apply-ds fun)
(combine-ds (map first group-by))))))
(defmacro ddply
([group-by fun]
`(ddply* ~(exprs-to-fns group-by) ~fun $data))
([group-by fun data]
`(ddply* ~(exprs-to-fns group-by) ~fun ~data)))
Saturday, June 8, 13

62.
Support functions - colwise
(ddply :Symbol
(colwise :num stats/mean)
tech-stocks)
Saturday, June 8, 13

63.
Support functions - transform
(ddply :Symbol
(transform :Change = (diff0 :Close)
:Date =* (time-format/parse
(time-format/formatters :year-month-day)
:Date))
tech-stocks)
Saturday, June 8, 13

64.
A Case Study
Saturday, June 8, 13

65.
A Case Study
“SpaceCurve delivers instantaneous
intelligence for location-based services,
commodities, defense, emergency
services and other markets. The
company is developing Big Data
solutions that continuously store and
immediately analyze massive amounts
of multidimensional data.”
Performance analysis of large-scale geospatial-
temporal ingest and query on the SpaceCurve
multidimensional DB
Saturday, June 8, 13

66.
Our Sample Problem
cpu23cpu11
cpu22cpu10
cpu09 cpu21
cpu20cpu08
cpu15
cpu16
cpu17
cpu14
cpu12
cpu19
cpu13
cpu18
cpu07
cpu06
cpu05
cpu04
cpu03
cpu02
cpu01
cpu00
cpu23cpu11
cpu22cpu10
cpu09 cpu21
cpu20cpu08
cpu15
cpu16
cpu17
cpu14
cpu12
cpu19
cpu13
cpu18
cpu07
cpu06
cpu05
cpu04
cpu03
cpu02
cpu01
cpu00
cpu23cpu11
cpu22cpu10
cpu09 cpu21
cpu20cpu08
cpu15
cpu16
cpu17
cpu14
cpu12
cpu19
cpu13
cpu18
cpu07
cpu06
cpu05
cpu04
cpu03
cpu02
cpu01
cpu00
cpu23cpu11
cpu22cpu10
cpu09 cpu21
cpu20cpu08
cpu15
cpu16
cpu17
cpu14
cpu12
cpu19
cpu13
cpu18
cpu07
cpu06
cpu05
cpu04
cpu03
cpu02
cpu01
cpu00
cpu23cpu11
cpu22cpu10
cpu09 cpu21
cpu20cpu08
cpu15
cpu16
cpu17
cpu14
cpu12
cpu19
cpu13
cpu18
cpu07
cpu06
cpu05
cpu04
cpu03
cpu02
cpu01
cpu00
cpu23cpu11
cpu22cpu10
cpu09 cpu21
cpu20cpu08
cpu15
cpu16
cpu17
cpu14
cpu12
cpu19
cpu13
cpu18
cpu07
cpu06
cpu05
cpu04
cpu03
cpu02
cpu01
cpu00
10GB/s/channel
switch
External Clients
10.0.1.101 10.0.1.102 10.0.1.107 10.0.1.109 10.0.1.111 10.0.1.112
‣CPU load data
‣6 systems
‣24 cores/each
‣6 data points
‣1 sample/second
‣~38 minutes run time
Total of ~2 million data points
Small subset of the overall SpaceCurve analysis
Saturday, June 8, 13

67.
Time to see it work...
Saturday, June 8, 13

68.
Where to?
Saturday, June 8, 13

69.
Where to?
Saturday, June 8, 13

70.
Where to?
• A full library implementation of Split-Apply-Combine and helpers
Saturday, June 8, 13

71.
Where to?
• A full library implementation of Split-Apply-Combine and helpers
• Add to Incanter?
Saturday, June 8, 13

72.
Where to?
• A full library implementation of Split-Apply-Combine and helpers
• Add to Incanter?
• Performance optimizations (mutable intermediate results, column-oriented
datasets)
Saturday, June 8, 13

73.
Where to?
• A full library implementation of Split-Apply-Combine and helpers
• Add to Incanter?
• Performance optimizations (mutable intermediate results, column-oriented
datasets)
• Implementation based on reducers and parallelism
Saturday, June 8, 13

74.
Where to?
• A full library implementation of Split-Apply-Combine and helpers
• Add to Incanter?
• Performance optimizations (mutable intermediate results, column-oriented
datasets)
• Implementation based on reducers and parallelism
• Explore the continuum from data exploration tools (R, Incanter) to large-scale
data analysis (Hadoop, Cascalog, SpaceCurve, etc.)
Saturday, June 8, 13

75.
Discussion
Saturday, June 8, 13

76.
References
• Source for this presentation: https://www.github.com/tomfaulhaber/split-
apply-combine
• The R Project: http://www.r-project.org
• The plyr home page: http://plyr.had.co.nz
• Hadley Wickham, The Split-Apply-Combine Strategy for Data Analysis,
Journal of Statistical Software, April 2011, Volume 40, Issue 1
• Incanter project: http://incanter.org
• Eric Rochester, The Clojure Data Analysis Cookbook, Packt Publishing, 2013
• Bruce Durling, Quick and Dirty Data Science with Incanter, talk from
EuroClojure 2012, http://confreaks.com/videos/2071-euroclojure2012-quick-
and-dirty-data-science-with-incanter
• Spacecurve: http://www.spacecurve.com
Tom Faulhaber
twitter: @tomfaulhaber
github: tomfaulhaber
Saturday, June 8, 13

77.
Photo Credits
• Florida Home - anoldent on flickr (http://www.flickr.com/photos/anoldent/2405722434/)
• Midland Coal Mine - jasonwoodhead23 on flickr (http://www.flickr.com/photos/woodhead/8522679843/)
• Paradise - Antti Simonen on flickr (http://www.flickr.com/photos/anttisimonen/6041095682/)
• Traders on the Exchange - thetaxhaven on flickr (http://www.flickr.com/photos/83532250@N06/7651028854)
• Louvre - dynamosquito on flickr (http://www.flickr.com/photos/25182210@N07/2802458437/)
• Construction - Aapo Haapanen on flickr (http://www.flickr.com/photos/decade_null/214247988/)
• Server farm - from the Spacecurve website (http://www.spacecurve.com)
• Sailboat race - Ryk Van Toronto on flickr (http://www.flickr.com/photos/sydandsaskia/394507351)
• Arguing Philosophers - David Schroeter on flickr (http://www.flickr.com/photos/53477785@N00/92134612/)
Saturday, June 8, 13