Building a Spam Detector with Naive Bayes Classifier

Spam detection is a critical task in natural language processing (NLP) and machine learning, aimed at identifying and filtering out unwanted or malicious messages. In this tutorial, we'll create a simple spam detector using the Naive Bayes classifier with Python's scikit-learn library.

Introduction

Spam detection plays a crucial role in email systems, messaging apps, and other communication platforms, as it helps users avoid irrelevant or harmful messages. Machine learning models, particularly the Naive Bayes classifier, are widely used for spam detection due to their simplicity and effectiveness.

Dataset Exploration

We'll start by loading the SMS Spam Collection dataset, which contains SMS messages labeled as 'spam' or 'ham' (not spam). Let's explore the dataset and visualize the distribution of spam and ham messages:

import pandas as pd
import matplotlib.pyplot as plt

# Load the dataset
df = pd.read_csv('SMSSpamCollection', sep='\t', names=['label', 'message'])

# Convert labels to binary (0 for ham, 1 for spam)
df['label'] = df['label'].map({'ham': 0, 'spam': 1})

# Visualize the distribution of spam and ham messages
spam_count = df['label'].sum()
ham_count = len(df) - spam_count

plt.figure(figsize=(6, 6))
plt.pie([ham_count, spam_count], labels=['Ham', 'Spam'], autopct='%1.1f%%', startangle=90)
plt.axis('equal')
plt.title('Distribution of Spam and Ham Messages')
plt.show()

The dataset contains a total of X messages, with Y% of them labeled as spam and Z% labeled as ham.

Data Preprocessing

Before training the model, we need to preprocess the text data. This involves removing punctuation, converting text to lowercase, and removing stopwords (common words that do not contribute much to the meaning of the text):

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

# Download stopwords if not already downloaded
nltk.download('stopwords')
nltk.download('punkt')

def preprocess_text(text):
    text = text.translate(str.maketrans('', '', string.punctuation))  # Remove punctuation
    text = text.lower()  # Convert text to lowercase
    stop_words = set(stopwords.words('english'))  # Get English stopwords
    word_tokens = word_tokenize(text)  # Tokenize text into words
    filtered_text = [word for word in word_tokens if word not in stop_words]  # Remove stopwords
    return ' '.join(filtered_text)

df['message'] = df['message'].apply(preprocess_text)

After preprocessing, each message in the dataset is cleaned and ready for further processing.

Feature Extraction

To train our model, we need to convert the text data into numerical features. We'll use the Bag-of-Words (BoW) model, which represents each message as a vector of word counts:

from sklearn.feature_extraction.text import CountVectorizer

count_vectorizer = CountVectorizer()
X = count_vectorizer.fit_transform(df['message'])
y = df['label']

The CountVectorizer converts a collection of text documents into a matrix of token counts, where each row represents a document and each column represents a unique word in the corpus.

Model Training and Evaluation

Next, we'll split the dataset into training and testing sets, and train a Multinomial Naive Bayes classifier:

from sklearn.model_selection import train_test_split
from sklearn.naive_bayes import MultinomialNB
from sklearn.metrics import accuracy_score, precision_score, recall_score, confusion_matrix

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)

nb_classifier = MultinomialNB()
nb_classifier.fit(X_train, y_train)

y_pred = nb_classifier.predict(X_test)

# Evaluate the model
accuracy = accuracy_score(y_test, y_pred)
precision = precision_score(y_test, y_pred)
recall = recall_score(y_test, y_pred)
conf_matrix = confusion_matrix(y_test, y_pred)

# Display evaluation metrics
print("Accuracy: {:.2f}%".format(accuracy * 100))
print("Precision: {:.2f}%".format(precision * 100))
print("Recall: {:.2f}%".format(recall * 100))
print("\nConfusion Matrix:")
print(conf_matrix)

Happy coding!

Give this code a try and share your thoughts in comments.