Text Preprocessing and Tokenization in Keras

Text preprocessing and tokenization are essential steps in natural language processing (NLP) tasks, including text classification, sentiment analysis, and machine translation. Keras, a popular deep learning library, provides efficient methods and tools to preprocess and tokenize textual data before training a model. In this article, we will explore the steps involved in text preprocessing and tokenization using Keras.

1. Text Preprocessing

Text preprocessing involves cleaning and preparing the text data before feeding it into a model. It includes several steps, such as:

a. Lowercasing

Lowercasing is the process of converting all letters in the text to lowercase. This step is often performed to ensure uniformity and avoid treating the same word differently based on its capitalization.

text = text.lower()

b. Removing Punctuation

Punctuation marks such as commas, periods, and quotation marks do not carry significant meaning in many NLP tasks. Removing them can help improve the efficiency and effectiveness of the model.

import string

text = text.translate(str.maketrans("", "", string.punctuation))

c. Removing Numbers

Numbers may not always contribute to the semantics of the text. Removing them can simplify the data and prevent the model from focusing on numerical values rather than the actual text.

text = ''.join(c for c in text if not c.isdigit())

d. Removing Stop Words

Stop words are commonly used words in a language, such as "the", "and", "is", etc., that do not carry much meaning in the context of NLP tasks. Removing them can help reduce noise in the data.

from nltk.corpus import stopwords
from nltk.tokenize import word_tokenize

stop_words = set(stopwords.words('english'))
tokens = word_tokenize(text)
filtered_text = [word for word in tokens if word not in stop_words]

e. Stemming and Lemmatization

Stemming and lemmatization are techniques used to reduce words to their base or root form. Stemming reduces a word to its stem, while lemmatization uses a vocabulary and morphological analysis to get to the root meaning of a word. These techniques help reduce vocabulary size and improve the model's understanding of the text.

from nltk.stem import PorterStemmer, WordNetLemmatizer

stemmer = PorterStemmer()
lemmatizer = WordNetLemmatizer()

stemmed_text = [stemmer.stem(word) for word in tokens]
lemmatized_text = [lemmatizer.lemmatize(word) for word in tokens]

2. Tokenization

Tokenization is the process of breaking down text into smaller units, such as words, phrases, or sentences, known as tokens. These tokens are easier to process and feed into a neural network.

In Keras, tokenization can be performed using the Tokenizer class. Here's an example:

from tensorflow.keras.preprocessing.text import Tokenizer

tokenizer = Tokenizer()

sequences = tokenizer.texts_to_sequences(texts)

The fit_on_texts method builds the vocabulary based on the given texts. The texts_to_sequences method converts each text into a sequence of integers, where each integer represents a unique token from the vocabulary.


Text preprocessing and tokenization are crucial steps in any NLP task. Keras provides powerful tools like the Tokenizer class to handle these steps efficiently. By properly preprocessing and tokenizing text data, you can improve the quality and performance of your NLP models. So, make sure to utilize these techniques before diving into the training process. Happy coding!

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