TF-IDF (TfidfVectorizer) in NLP - ML Experiment: Train & Evaluate

Experiment - TF-IDF (TfidfVectorizer)

Problem:You want to convert a collection of text documents into numbers that show how important each word is in each document. You are using TF-IDF to do this.

Current Metrics:The current TF-IDF vectorizer uses default settings and creates very large feature vectors with many unimportant words included.

Issue:The model is slow and the vectors are too large because many common words that do not help distinguish documents are included.

Your Task

Improve the TF-IDF vectorizer by reducing the number of features while keeping important words, to make the vectors smaller and more meaningful.

You must use TfidfVectorizer from sklearn.

You cannot remove the TF-IDF method itself.

You should not reduce the dataset size.

Hint 1

Hint 2

Hint 3

Solution

NLP

from sklearn.feature_extraction.text import TfidfVectorizer

# Sample documents
texts = [
    "The cat sat on the mat.",
    "The dog ate my homework.",
    "Cats and dogs are great pets.",
    "I love my pet cat."
]

# Improved TF-IDF vectorizer with stop words removal and max features
vectorizer = TfidfVectorizer(stop_words='english', max_features=10)

# Fit and transform the texts
X = vectorizer.fit_transform(texts)

# Show feature names and the TF-IDF matrix shape
features = vectorizer.get_feature_names_out()
shape = X.shape

print(f"Features: {features}")
print(f"TF-IDF matrix shape: {shape}")

Added stop_words='english' to remove common words like 'the', 'and', 'is'.

Set max_features=10 to limit the number of features to the 10 most important words.

Results Interpretation

Before: TF-IDF matrix shape was (4, 20) with many common and rare words included.

After: TF-IDF matrix shape is (4, 10) with stop words removed and rare words ignored.

Removing stop words and limiting features helps create smaller, more meaningful TF-IDF vectors that improve model speed and focus on important words.

Bonus Experiment

Try using n-grams (like bigrams) in the TF-IDF vectorizer to capture word pairs and see if it improves text representation.

💡 Hint

Set the 'ngram_range' parameter to (1, 2) in TfidfVectorizer to include single words and pairs of words.

Practice

1. What does the TfidfVectorizer primarily do in text processing?

easy

A. It converts text into numbers reflecting word importance.

B. It translates text into another language.

C. It removes all punctuation from the text.

D. It counts the total number of characters in text.

Solution

1. Step 1: Understand the purpose of TfidfVectorizer

   TfidfVectorizer transforms text data into numerical values that represent how important each word is in the text.

2. Step 2: Compare options with this purpose

   Only It converts text into numbers reflecting word importance. describes converting text into numbers that reflect word importance, which matches the function of TfidfVectorizer.

3. Final Answer:

   It converts text into numbers reflecting word importance. -> Option A

4. Quick Check:

   TF-IDF = word importance numbers [OK]

Hint: TF-IDF = numbers showing word importance in text [OK]

Common Mistakes:

• Confusing TF-IDF with translation or punctuation removal
• Thinking TF-IDF counts characters instead of words
• Assuming TF-IDF just counts word frequency without weighting

2. Which of the following is the correct way to import TfidfVectorizer from scikit-learn?

easy

A. from sklearn.feature_extraction.text import TfidfVectorizer

B. import TfidfVectorizer from sklearn.text

C. from sklearn.text import TfidfVectorizer

D. import TfidfVectorizer from sklearn.feature_extraction

Solution

1. Step 1: Recall the correct module for TfidfVectorizer

   TfidfVectorizer is located in sklearn.feature_extraction.text module.

2. Step 2: Match the correct import syntax

   The correct Python import syntax is: from sklearn.feature_extraction.text import TfidfVectorizer, which matches from sklearn.feature_extraction.text import TfidfVectorizer.

3. Final Answer:

   from sklearn.feature_extraction.text import TfidfVectorizer -> Option A

4. Quick Check:

   Correct import path = from sklearn.feature_extraction.text import TfidfVectorizer [OK]

Hint: Remember sklearn.feature_extraction.text for TfidfVectorizer import [OK]

Common Mistakes:

• Using wrong module names like sklearn.text
• Incorrect import syntax order
• Trying to import from sklearn.feature_extraction without .text

3. What will be the shape of the output matrix after applying TfidfVectorizer on 3 documents with 5 unique words total?

medium

A. (5, 5)

B. (5, 3)

C. (3, 3)

D. (3, 5)

Solution

1. Step 1: Understand TfidfVectorizer output shape

   The output is a matrix where rows represent documents and columns represent unique words (features).

2. Step 2: Apply to given numbers

   With 3 documents and 5 unique words, the shape is (3, 5) -- 3 rows and 5 columns.

3. Final Answer:

   (3, 5) -> Option D

4. Quick Check:

   Output shape = (documents, unique words) = (3, 5) [OK]

Hint: Rows = documents, columns = unique words in TF-IDF matrix [OK]

Common Mistakes:

• Swapping rows and columns in output shape
• Confusing number of documents with number of words
• Assuming square matrix regardless of input

4. Given this code snippet, what is the error?

from sklearn.feature_extraction.text import TfidfVectorizer
texts = ['apple orange', 'orange banana', 'banana apple']
vectorizer = TfidfVectorizer()
X = vectorizer.fit_transform(texts)
print(X.shape)
print(vectorizer.get_feature_names())

medium

A. fit_transform() requires a list of integers, not strings

B. get_feature_names() is deprecated; should use get_feature_names_out()

C. TfidfVectorizer() needs a parameter specifying language

D. print(X.shape) will cause an error because X is not defined

Solution

1. Step 1: Check method usage for feature names

   In recent scikit-learn versions, get_feature_names() is deprecated and replaced by get_feature_names_out().

2. Step 2: Verify other code parts

   fit_transform() accepts list of strings, TfidfVectorizer() works without language parameter, and X is defined correctly.

3. Final Answer:

   get_feature_names() is deprecated; should use get_feature_names_out() -> Option B

4. Quick Check:

   Use get_feature_names_out() instead of deprecated get_feature_names() [OK]

Hint: Use get_feature_names_out() for feature names in new sklearn versions [OK]

Common Mistakes:

• Using deprecated get_feature_names() causing warnings or errors
• Thinking fit_transform() needs numeric input
• Assuming language parameter is mandatory

5. You want to ignore very common words like 'the' and 'is' when using TfidfVectorizer. Which parameter helps you do this effectively?

hard

A. lowercase=false

B. max_features=1000

C. stop_words='english'

D. norm=null

Solution

1. Step 1: Identify parameter for ignoring common words

   The stop_words parameter removes common words (stop words) like 'the', 'is', 'and'. Setting stop_words='english' removes English stop words.

2. Step 2: Check other parameters

   max_features limits number of features but doesn't remove stop words; lowercase controls case; norm controls normalization, none remove stop words.

3. Final Answer:

   stop_words='english' -> Option C

4. Quick Check:

   stop_words='english' removes common words [OK]

Hint: Use stop_words='english' to skip common words [OK]

Common Mistakes:

• Confusing max_features with stop words removal
• Not using stop_words parameter at all
• Thinking lowercase removes stop words