Welcome to this tutorial! Our goal is to learn about text classification, a crucial aspect of Natural Language Processing (NLP), and how to implement it using the Python library scikit-learn. By the end of this tutorial, you will be able to categorize a body of text into predefined classes.
What will you learn?
Prerequisites:
Text Classification is a machine learning technique that automatically classifies text documents into predefined categories. This is useful in many areas like spam filtering, sentiment analysis, and topic labeling.
To perform text classification using scikit-learn, we first need to convert text into a format that can be understood by our machine learning algorithms, typically numerical. This process is called feature extraction or vectorization.
Best practices and tips
from sklearn.feature_extraction.text import CountVectorizer
from sklearn.naive_bayes import MultinomialNB
from sklearn.model_selection import train_test_split
# Sample text data
X = ["This is the first document", "This document is the second document", "And this is the third one"]
y = [0, 1, 1] # Classes
# Convert text to numerical data
vectorizer = CountVectorizer()
X = vectorizer.fit_transform(X)
# Split data into training and test sets
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
# Train the model
clf = MultinomialNB()
clf.fit(X_train, y_train)
# Test the model
print(clf.predict(vectorizer.transform(["This is the first document"])))
In this example, we first convert the text into numerical data using CountVectorizer. Then, we split our data into a training set and a test set. We train our model using MultinomialNB, a Naive Bayes classifier suitable for classification with discrete features (like word counts for text classification).
from sklearn.feature_extraction.text import TfidfVectorizer
from sklearn.naive_bayes import MultinomialNB
from sklearn.model_selection import train_test_split
# Sample text data
X = ["This is the first document", "This document is the second document", "And this is the third one"]
y = [0, 1, 1] # Classes
# Convert text to numerical data
vectorizer = TfidfVectorizer()
X = vectorizer.fit_transform(X)
# Split data into training and test sets
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
# Train the model
clf = MultinomialNB()
clf.fit(X_train, y_train)
# Test the model
print(clf.predict(vectorizer.transform(["This is the first document"])))
In this second example, we use TfidfVectorizer instead of CountVectorizer. TfidfVectorizer considers the overall document weightage of a word. It helps us understand the context and eliminates the most common words.
In this tutorial, we learned about Text Classification and how to implement it using the scikit-learn library. We also explored how to prepare text data for machine learning and the importance of splitting our dataset into training and test sets.
Next, you might want to explore other feature extraction techniques or try implementing text classification using different classifiers. For more information, check out the scikit-learn documentation.
Exercise 1: Implement Text Classification using CountVectorizer and a different classifier from MultinomialNB.
Exercise 2: Implement Text Classification with a larger dataset. Try using the 20 Newsgroups dataset available in scikit-learn's datasets.
Exercise 3: Implement Text Classification using TfidfVectorizer and evaluate the model's performance using different evaluation metrics like precision, recall, and F1-score.
Remember, the key to mastering Text Classification or any machine learning algorithm is practice. Keep experimenting!