Text Preprocessing

In natural language processing, text preprocessing is the practice of cleaning and preparing text data. NLTK and re are common Python libraries used to handle many text preprocessing tasks.

Noise Removal

In natural language processing, noise removal is a text preprocessing task devoted to stripping text of formatting.

import re

text = "Five fantastic fish flew off to find faraway functions. Maybe find another five fantastic fish? Find my fish with a function please!"

# remove punctuation
result = re.sub(r'[\.\?\!\,\:\;\"]', '', text)

print(result)
# Five fantastic fish flew off to find faraway functions Maybe find another five fantastic fish Find my fish with a function please

Tokenization

In natural language processing, tokenization is the text preprocessing task of breaking up text into smaller components of text (known as tokens).

from nltk.tokenize import word_tokenize

text = "This is a text to tokenize"
tokenized = word_tokenize(text)

print(tokenized)
# ["This", "is", "a", "text", "to", "tokenize"]

Text Normalization

In natural language processing, normalization encompasses many text preprocessing tasks including stemming, lemmatization, upper or lowercasing, and stopwords removal.

Stemming

In natural language processing, stemming is the text preprocessing normalization task concerned with bluntly removing word affixes (prefixes and suffixes).

from nltk.stem import PorterStemmer

tokenized = ["So", "many", "squids", "are", "jumping"]

stemmer = PorterStemmer()
stemmed = [stemmer.stem(token) for token in tokenized]

print(stemmed)
# ['So', 'mani', 'squid', 'are', 'jump']

Lemmatization

In natural language processing, lemmatization is the text preprocessing normalization task concerned with bringing words down to their root forms.

from nltk.stem import WordNetLemmatizer

tokenized = ["So", "many", "squids", "are", "jumping"]

lemmatizer = WordNetLemmatizer()
lemmatized = [lemmatizer.lemmatize(token) for token in tokenized]

print(stemmed)
# ['So', 'many', 'squid', 'be', 'jump']

Stopword Removal

In natural language processing, stopword removal is the process of removing words from a string that don’t provide any information about the tone of a statement.

from nltk.corpus import stopwords 

# define set of English stopwords
stop_words = set(stopwords.words('english')) 

# remove stopwords from tokens in dataset
statement_no_stop = [word for word in word_tokens if word not in stop_words]

Part-of-Speech Tagging

In natural language processing, part-of-speech tagging is the process of assigning a part of speech to every word in a string. Using the part of speech can improve the results of lemmatization.

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Text Preprocessing