R practical

1. R - Practice

2. > 1 + 1
[1] 2
-----------
> 100:130
[1] 100 101 102 103 104 105 106 107 108 109 110 111 112 [14] 113
114 115 116 117 118 119 120 121 122 123 124 125 [25] 126 127 128
129 130

3. Error
> 3 % 5
Error: unexpected input in "3 % 5“
------
If you type an incomplete command and press Enter, R will display a + prompt,
which means it is waiting for you to type the rest of your command. Either finish
the command or hit Escape to start over:
> 5 -
+
+
1
[1] 4

4. Objects
R lets you save data by storing it inside an R object.
What’s an object?
Just a name that you can use to call up stored data. For example, you
can save data into an object like a or b
a <- 1
a # output: 1
a + 2 # output : 3

5. Object creation
< followed by –
die <- 1:6
die # Output: 1 2 3 4 5 6
Rules for Object creation:
name an object in R almost anything you want, but there are a few rules.
First, a name cannot start with a number.
Second, a name cannot use some special symbols, like ^, !, $, @, +, -, /, or *

6. Case sensitive
• R also understands capitalization (or is case-sensitive), so name and
Name will refer to different objects:
Name <- 1
name <- 0
Name + 1 # Output: 2

7. List of Objects ls()
Find object names you have already used with the function using ls:
ls()
#Output: "a" "die" "my_number" "name" "Name"

8. die <- 1:6
die - 1 ## 0 1 2 3 4 5
die / 2 ## 0.5 1.0 1.5 2.0 2.5 3.0
die * die ## 1 4 9 16 25 36

9. die ## 1 2 3 4 5 6
die + 1:2 ## 2 4 4 6 6 8 - HOW?

10. R will repeat a short vector to do element-wise
operations with two vectors of uneven lengths

11. Warning
die + 1:4 ## 2 4 6 8 6 8
Warning message: In die + 1:4 : longer object length is not a multiple of
shorter object length

12. Creating Matrices For Multiplication
inner multiplication with the %*% operator
outer multiplication with the %o% operator

13. %*% - inner multiplication
die %*% die
Output: 91 - the output has been generated as a vector
die %o% die
Output:
[,1] [,2] [,3] [,4] [,5] [,6]
[1,] 1 2 3 4 5 6
--the output has been generated as a matrix of one row and one column

16. Functions
R comes with many functions for tasks like random sampling.
round a number with the round function,
calculate its factorial with the factorial function.
round(3.1415)
## 3
factorial(3)
## 6

17. Functions with Arguments
 The data that you pass into the function is called the function’s argument.
 The argument can be raw data, an R object, or even the results of another R
function.
 R will work from the innermost function to the outermost
mean(1:6)
## 3.5
mean(die)
## 3.5
round(mean(die))
## 4

18. • simulate a roll of the die with R’s sample function
sample(x = 1:4, size = 2)
## 3 2
Try:
die=1:6
sample(x = die, size = 1)
sample(size = 1, x = die) ## output random sample between 1 to 6
two arguments: a vector named x and a number named size
Note: Many R functions take multiple arguments

19. Writing Your Own Functions
die <- 1:6
dice <- sample(die, size = 2, replace = TRUE)
sum(dice)