Lemmatization in spaCy in NLP

Introduction

Lemmatization helps find the base form of words. It makes text easier to analyze by treating different forms of a word as one.

When you want to count how often a word appears, ignoring its different forms.

When you need to compare words in their simplest form for search or matching.

When cleaning text data before training a language model.

When analyzing text to find the main meaning without extra word endings.

Syntax

NLP

import spacy

nlp = spacy.load('en_core_web_sm')
doc = nlp('running runs ran')
lemmas = [token.lemma_ for token in doc]

Use token.lemma_ to get the base form (lemma) of each word.

Make sure to load a spaCy language model like en_core_web_sm before lemmatization.

Examples

This example shows lemmatization of plural and verb forms.

NLP

import spacy

nlp = spacy.load('en_core_web_sm')
doc = nlp('cats are running')
lemmas = [token.lemma_ for token in doc]
print(lemmas)

Lemmatization also handles irregular forms like comparative and superlative adjectives.

NLP

import spacy

nlp = spacy.load('en_core_web_sm')
doc = nlp('better best good')
lemmas = [token.lemma_ for token in doc]
print(lemmas)

Sample Model

This program loads spaCy's English model, processes a sentence, and prints the base forms of each word.

NLP

import spacy

# Load English model
nlp = spacy.load('en_core_web_sm')

# Text with different word forms
text = 'The children are playing and played in the playground.'

doc = nlp(text)

# Extract lemmas
lemmas = [token.lemma_ for token in doc]

print('Original text:', text)
print('Lemmatized tokens:', lemmas)

Important Notes

Lemmatization depends on the word's context, so spaCy uses part-of-speech tags to get accurate lemmas.

Stop words like 'the' keep their lemma as is because they are already base forms.

Summary

Lemmatization finds the base form of words to simplify text analysis.

Use token.lemma_ in spaCy after loading a language model.

It helps treat different word forms as the same word for better understanding.

Practice

1. What does lemmatization do in natural language processing using spaCy?

easy

A. It removes all punctuation from the text.

B. It counts the number of words in a sentence.

C. It finds the base or dictionary form of a word.

D. It translates text into another language.

Solution

1. Step 1: Understand the purpose of lemmatization

   Lemmatization simplifies words by converting them to their base form, like 'running' to 'run'.

2. Step 2: Compare options to definition

   Only It finds the base or dictionary form of a word. correctly describes finding the base or dictionary form of a word.

3. Final Answer:

   It finds the base or dictionary form of a word. -> Option C

4. Quick Check:

   Lemmatization = base form extraction [OK]

Hint: Lemmatization = find base word form [OK]

Common Mistakes:

• Confusing lemmatization with token counting
• Thinking it translates text
• Mixing it up with punctuation removal

2. Which of the following is the correct way to get the lemma of a token in spaCy?

easy

A. token.lemma_

B. token.lemma

C. token.lemmatize()

D. token.get_lemma()

Solution

1. Step 1: Recall spaCy token attribute for lemma

   spaCy uses the attribute lemma_ (with underscore) to get the lemma as a string.

2. Step 2: Check each option

   token.lemma_ matches the correct attribute. token.lemma, token.lemmatize(), and token.get_lemma() are not valid spaCy syntax.

3. Final Answer:

   token.lemma_ -> Option A

4. Quick Check:

   spaCy lemma attribute = token.lemma_ [OK]

Hint: Use token.lemma_ with underscore for lemma string [OK]

Common Mistakes:

• Using token.lemma without underscore
• Trying to call a method like lemmatize()
• Using non-existent methods like get_lemma()

3. Given the code snippet:

import spacy
nlp = spacy.load('en_core_web_sm')
doc = nlp('The cats are running fast')
lemmas = [token.lemma_ for token in doc]

What is the value of lemmas?

medium

A. ['the', 'cats', 'are', 'running', 'fast']

B. ['The', 'cats', 'are', 'running', 'fast']

C. ['The', 'cat', 'is', 'run', 'fast']

D. ['the', 'cat', 'be', 'run', 'fast']

Solution

1. Step 1: Understand spaCy lemmatization output

   spaCy converts words to their base forms: 'cats' to 'cat', 'are' to 'be', 'running' to 'run', and lowercases 'The' to 'the'.

2. Step 2: Match the list of lemmas

   ['the', 'cat', 'be', 'run', 'fast'] matches the expected lemmas: ['the', 'cat', 'be', 'run', 'fast'].

3. Final Answer:

   ['the', 'cat', 'be', 'run', 'fast'] -> Option D

4. Quick Check:

   spaCy lemma list = ['the', 'cat', 'be', 'run', 'fast'] [OK]

Hint: Lemmas are base forms, usually lowercase [OK]

Common Mistakes:

• Expecting original words instead of lemmas
• Not lowercasing lemmas
• Confusing verb forms like 'are' with 'is'

4. Identify the error in this spaCy lemmatization code:

import spacy
nlp = spacy.load('en_core_web_sm')
doc = nlp('She was eating apples')
lemmas = [token.lemma for token in doc]
print(lemmas)

medium

A. Missing parentheses in spacy.load()

B. Using token.lemma instead of token.lemma_

C. Incorrect model name in spacy.load()

D. Missing import for lemmatizer

Solution

1. Step 1: Check spaCy lemma attribute usage

   spaCy tokens have lemma_ (with underscore) for lemma string, not lemma.

2. Step 2: Identify the error in code

   The code uses token.lemma which returns a property object, not the lemma string, causing wrong output.

3. Final Answer:

   Using token.lemma instead of token.lemma_ -> Option B

4. Quick Check:

   Use token.lemma_ for lemma string [OK]

Hint: Remember underscore in token.lemma_ for lemma [OK]

Common Mistakes:

• Using token.lemma without underscore
• Assuming spacy.load needs parentheses missing
• Thinking model name is wrong

5. You want to lemmatize a list of sentences and count how many times the lemma 'run' appears using spaCy. Which code snippet correctly does this?

hard

A. import spacy
nlp = spacy.load('en_core_web_sm')
sentences = ['I run daily', 'He is running fast']
count = 0
for sent in sentences:
doc = nlp(sent)
count += sum(token.lemma_ == 'run' for token in doc)
print(count)

B. import spacy
nlp = spacy.load('en_core_web_sm')
sentences = ['I run daily', 'He is running fast']
count = 0
for sent in sentences:
doc = nlp(sent)
count += sum(token.text == 'run' for token in doc)
print(count)

C. import spacy
nlp = spacy.load('en_core_web_sm')
sentences = ['I run daily', 'He is running fast']
count = 0
for sent in sentences:
doc = nlp(sent)
count += sum(token.lemma == 'run' for token in doc)
print(count)

D. import spacy
nlp = spacy.load('en_core_web_sm')
sentences = ['I run daily', 'He is running fast']
count = 0
for sent in sentences:
doc = nlp(sent)
count += sum(token.lemma_ == 'running' for token in doc)
print(count)

Solution

1. Step 1: Understand the goal and spaCy usage

   We want to count all tokens whose lemma is 'run', so we must use token.lemma_ and compare to 'run'.

2. Step 2: Analyze each option

   import spacy nlp = spacy.load('en_core_web_sm') sentences = ['I run daily', 'He is running fast'] count = 0 for sent in sentences: doc = nlp(sent) count += sum(token.lemma_ == 'run' for token in doc) print(count) correctly uses token.lemma_ == 'run'. import spacy nlp = spacy.load('en_core_web_sm') sentences = ['I run daily', 'He is running fast'] count = 0 for sent in sentences: doc = nlp(sent) count += sum(token.text == 'run' for token in doc) print(count) compares original text, missing 'running'. import spacy nlp = spacy.load('en_core_web_sm') sentences = ['I run daily', 'He is running fast'] count = 0 for sent in sentences: doc = nlp(sent) count += sum(token.lemma == 'run' for token in doc) print(count) uses token.lemma without underscore, which is incorrect. import spacy nlp = spacy.load('en_core_web_sm') sentences = ['I run daily', 'He is running fast'] count = 0 for sent in sentences: doc = nlp(sent) count += sum(token.lemma_ == 'running' for token in doc) print(count) compares lemma to 'running', which is not the base form.

3. Final Answer:

   sum(token.lemma_ == 'run' for token in doc) -> Option A

4. Quick Check:

   Count lemma 'run' using token.lemma_ == 'run' [OK]

Hint: Compare token.lemma_ to base word for counting [OK]

Common Mistakes:

• Comparing token.text instead of token.lemma_
• Using token.lemma without underscore
• Comparing lemma to non-base form like 'running'