It's a brief overview of Natural Language Processing using Python module NLTK.The codes for demonstration can be found from the github link given in the references slide.

1. Natural Language Processing
Using Python
Presented by:-
Sumit Kumar Raj
1DS09IS082
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2. Table of Contents
•
Introduction
•
History
•
Methods in NLP
•
Natural Language Toolkit
•
Sample Codes
•
Feeling Lonely ?
•
Building a Spam Filter
•
Applications
•
References
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3. What is Natural Language Processing ?
•Computer aided text analysis of human language.
•The goal is to enable machines to understand human
language and extract meaning from text.
•It is a field of study which falls under the category of
machine learning and more specifically computational
linguistics.
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4. History
•
1948- 1st NLP application
– dictionary look-up system
– developed at Birkbeck College, London
•
l 1949- American interest
–WWII code breaker Warren Weaver
– He viewed German as English in code.
•
1966- Over-promised under-delivered
– Machine Translation worked only word by word
l
– NLP brought the first hostility of research funding
l
– NLP gave AI a bad name before AI had a name.
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5. Natural language processing is heavily used throughout all web
technologies
Search engines
Consumer behavior analysis Site recommendations
Sentiment analysis Spam filtering
Automated customer Knowledge bases and
support systems expert systems
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6. Context
Little sister: What’s your name?
Me: Uhh….Sumit..?
Sister: Can you spell it?
Me: yes. S-U-M-I-T…..
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7. Sister: WRONG! It’s spelled “I-
T”
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8. Ambiguity
“I shot the man with ice cream.“
-
A man with ice cream was shot
-
A man had ice cream shot at him
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9. Methods :-
1) POS Tagging :-
•In corpus linguistics, Parts-of-speech tagging also called
grammatical tagging or word-category disambiguation.
•It is the process of marking up a word in a text corres-
ponding to a particular POS.
•POS tagging is harder than just having a list of words
and their parts of speech.
•Consider the example:
l
The sailor dogs the barmaid.
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10. 2) Parsing :-
•In
context of NLP, parsing may be defined as the process of
assigning structural descriptions to sequences of words in
a natural language.
Applications of parsing include
simple phrase finding, eg. for proper name recognition
Full semantic analysis of text, e.g. information extraction or
machine translation
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11. 3) Speech Recognition:-
•
It is concerned with the mapping a continuous speech signal
into a sequence of recognized words.
•
Problem is variation in pronunciation, homonyms.
•
In sentence “the boy eats”, a bi-gram model sufficient to
model the relationship b/w boy and eats.
“The boy on the hill by the lake in our town…eats”
•
Bi-gram and Trigram have proven extremely effective in
obvious dependencies.
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12. 4) Machine Translation:-
•
It involves translating text from one NL to another.
•
Approaches:-
-simple word substitution,with some changes in ordering to
account for grammatical differences
-translate the source language into underlying meaning
representation or interlingua
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13. 5) Stemming:-
•
In linguistic morphology and information retrieval, stemming is
the process for reducing inflected words to their stem.
•
The stem need not be identical to the morphological root of the
word.
•
Many search engines treat words with same stem as synonyms
as a kind of query broadening, a process called conflation.
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14. Natural Language Toolkit
•
NLTK is a leading platform for building Python program to
work with human language data.
•
Provides a suite of text processing libraries for
classification, tokenization, stemming, tagging, parsing,
and semantic reasoning.
•
Currently only available for Python 2.5 – 2.6
http://www.nltk.org/download
•
`easy_install nltk
•
Prerequisites
–
NumPy
–
SciPy
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15. Let’s dive into some code!
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16. Part of Speech Tagging
from nltk import pos_tag,word_tokenize
sentence1 = 'this is a demo that will show you how
to detects parts of speech with little effort
using NLTK!'
tokenized_sent = word_tokenize(sentence1)
print pos_tag(tokenized_sent)
[('this', 'DT'), ('is', 'VBZ'), ('a', 'DT'), ('demo', 'NN'), ('that', 'WDT'),
('will', 'MD'), ('show', 'VB'), ('you', 'PRP'), ('how', 'WRB'), ('to', 'TO'),
('detects', 'NNS'), ('parts', 'NNS'), ('of', 'IN'), ('speech', 'NN'), ('with',
'IN'), ('little', 'JJ'), ('effort', 'NN'), ('using', 'VBG'), ('NLTK', 'NNP'),('!',
'.')]
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17. Fun things to Try
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18. Feeling lonely?
Eliza is there to talk to you all day! What human could ever do that
for you??
from nltk.chat import eliza
eliza.eliza_chat()
……starts the chatbot
Therapist
---------
Talk to the program by typing in plain English, using normal upper-
and lower-case letters and punctuation. Enter "quit" when done.
============================================================
============
Hello. How are you feeling today?
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19. Let’s build something even
cooler
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20. Lets write a Spam filter!
A program that analyzes legitimate emails “Ham” as well as
“Spam” and learns the features that are associated with
each.
Once trained, we should be able to run this program on
incoming mail and have it reliably label each one with the
appropriate category.
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21. “Spambot.py” (continued)
1. Extract one of the archives from the site into your working directory.
2. Create a python script, lets call it “spambot.py”.
Your working directory should contain the “spambot” script and the
3.
folders “spam” and “ham”.
from nltk import word_tokenize,
WordNetLemmatizer,NaiveBayesClassifier
,classify,MaxentClassifier
from nltk.corpus import stopwords
import random
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22. “Spambot.py” (continued)
label each item with the appropriate label and store them as a list of tuples
mixedemails = ([(email,'spam') for email in spamtexts]
mixedemails += [(email,'ham') for email in hamtexts])
From this list of random but labeled emails, we will defined a “feature
extractor” which outputs a feature set that our program can use to statistically
compare spam and ham.
random.shuffle(mixedemails)
lets give them a nice shuffle
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23. “Spambot.py” (continued)
def email_features(sent):
features = {}
wordtokens = [wordlemmatizer.lemmatize(word.lower()) for
word in word_tokenize(sent)] Normalize words
for word in wordtokens:
if word not in commonwords:
features[word] = True
return features
If the word is not a stop-word then lets
consider it a “feature”
featuresets = [(email_features(n), g) for (n,g) in mixedemails]
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24. “Spambot.py” (continued)
While True:
featset = email_features(raw_input("Enter text to classify: "))
print classifier.classify(featset)
We can now directly input new email and have it classified as either Spam or
Ham
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25. Applications :-
•
Conversion from natural language to computer language
and vice-versa.
•
Translation from one human language to another.
•
Automatic checking for grammar and writing techniques.
•
Spam filtering
•
Sentiment Analysis
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26. Conclusion:-
NLP takes a very important role in new machine human interfaces. When we look at
Some of the products based on technologies with NLP we can see that they are very
advanced but very useful.
But there are many limitations, For example language we speak is highly ambiguous.
This makes it very difficult to understand and analyze. Also with so many languages
spoken all over the world it is very difficult to design a system that is 100% accurate.
These problems get more complicated when we think of different people speaking the
same language with different styles.
Intelligent systems are being experimented right now.
We will be able to see improved applications of NLP in the near future.
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27. References :-
•
http://en.wikipedia.org/wiki/Natural_language_processing
•
An overview of Empirical Natural Language Processing
by Eric Brill and Raymond J. Mooney
•
Investigating classification for natural language processing tasks
by Ben W. Medlock, University of Cambridge
•
Natural Language Processing and Machine Learning using Python
by Shankar Ambady.
•
http://www.slideshare.net
•
http://www.doc.ic.ac.uk/~nd/surprise_97/journal/vol1/hks/index.html
l
http://googlesystem.blogspot.in/2012/10/google-improves-results-for-natural/
Codes from :https://github.com/shanbady/NLTK-Boston-Python-Meetup
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28. Any Questions ???
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29. Thank You...
Reach me @:
facebook.com/sumit12dec
sumit786raj@gmail.com
9590 285 524
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