Lemmatization — Everything You Need To Get Started

by | Dec 9, 2022 | Natural Language Processing

Lemmatization is the conversion of a word to its base form or lemma. This is different from stemming, which is the process of taking a word down to its root form by removing its prefixes and suffixes. Lemmatization, on the other hand, considers the context and meaning of a word and tries to convert it to a format that is more meaningful and easier to work with.

For example, the words “was,” “is,” and “will be” can all be lemmatized to the word “be.” Similarly, the words “better” and “best” can be lemmatized to the word “good.”

Lemmatization reduces a text to it's root words

Lemmatization reduces text down to it’s root making it easier to find keywords.

What is lemmatization?

Lemmatization is commonly used in natural language processing (NLP) and information retrieval applications, where it can improve the accuracy and performance of text analysis and search algorithms. By converting words to their base form, lemmatization can reduce the dimensionality of the text data and allow the algorithms to focus on the most critical and relevant information in the text.

There are many different tools and libraries available for performing lemmatization in Python. Some popular examples include NLTK, SpaCy, and Gensim. To use these libraries for lemmatization, you will typically need first to tokenize the text into individual words and then apply the lemmatization function to each token.

What is stemming?

Stemming is reducing a word to its root form, typically by removing prefixes and suffixes. This is a common technique used in natural language processing (NLP) and information retrieval applications, where it can help reduce the complexity and noise in the text data and make it easier to work with.

For example, the words “aggressively,” “aggressiveness,” and “aggressor” can all be stemmed to the word “aggress,” which is the root form of these words. Similarly, the words “universities” and “university” can be stemmed to the word “univers,” which is the root form of these words.

Difference between stemming and lemmatization

Lemmatization and stemming reduce words to their base form or root form. However, there are some essential differences between these two approaches.

Stemming typically involves removing prefixes and suffixes from a word and sometimes even modifying its internal structure to reduce it to its root form. This can be a simple and efficient way to normalize text, but it often produces words that need to be validated or meaningful. For example, the word “aggressively” might stem from “aggress,” which is not valid in English.

Lemmatization, on the other hand, considers the context and meaning of a word and tries to convert it to a form that is more meaningful and easier to work with. This typically involves using a vocabulary and morphological analysis of the words to identify the lemma of each word. For example, the words “was,” “is,” and “will be” can all be lemmatized to the word “be,” and the words “better” and “best” can be lemmatized to the word “good.”

In general, lemmatization is more sophisticated and accurate than stemming, but it can also be more computationally expensive. Whether to use stemming, lemmatization or a combination of both depends on your application’s specific requirements and goals.

Practical use cases of lemmatization

Lemmatization is a technique to reduce words to their base form, or lemma. This can be useful in many natural language processing (NLP) and information retrieval applications, improving the accuracy and performance of text analysis and search algorithms.

Some practical applications of lemmatization include:

  • Text classification: Lemmatization can help improve the performance of text classification algorithms and keyword extraction by reducing the number of unique words in the text and making the text more consistent and coherent. This can make it easier for the algorithm to identify the most important features and patterns in the text and assign it to the correct category or label.
  • Sentiment analysis: Lemmatization can help improve the accuracy of sentiment analysis algorithms by converting words with multiple forms, such as “good,” “better,” and “best,” to their base form, “good.” This can reduce the noise and variability in the text and allow the algorithm to focus on the most relevant and informative words and phrases.
  • Topic modelling: Lemmatization can improve the quality and interpretability of topic models by reducing the dimensionality of the text data and removing irrelevant and redundant words. This can make the topics more coherent and meaningful and make it easier to understand and visualize the main themes and ideas in the text.
  • Information retrieval: Lemmatization can help improve the accuracy and relevance of search results by converting query terms and document words to their base form. This can reduce the number of false positives and false negatives and make the search results more consistent and relevant to the user’s needs.

Overall, lemmatization can be valuable in many NLP and information retrieval applications. For example, it can help reduce the complexity and noise in the text data and improve the performance and accuracy of text analysis and search algorithms.

Examples of lemmatization in Python

To perform lemmatization in Python, you can use one of the many natural language processing (NLP) libraries available. Some popular examples include NLTK, spaCy, and Gensim.

NLTK lemmatizer

Note that you will need to first install NLTK and download its WordNet data before running this example. You can do this by running the following commands in your Python interpreter:

import nltk nltk.download('wordnet')

Here is an example of how you can use NLTK for lemmatization in Python:

import nltk 
from nltk.stem import WordNetLemmatizer 

# Define a text string 
text = "This is a sample text. It contains some words that we can use for lemmatization." 

# Tokenize the text into individual words 
tokens = nltk.word_tokenize(text) 

# Create a WordNetLemmatizer object 
lemmatizer = WordNetLemmatizer() 

# Lemmatize each word and print the result 
for token in tokens: 
  lemma = lemmatizer.lemmatize(token) 
  print(token, "-->", lemma)

In this example, the WordNetLemmatizer class from NLTK will lemmatize each word in the text and print the result. For example, the word “contains” will be lemmatized to “contain,” and the word “words” will be lemmatized to “word.”

SpaCy lemmatizer

Alternatively, you can use the SpaCy library for lemmatization in Python.

First install spaCy and download its English language model before running this example. You can do this by running the following commands on the command line:

pip install spacy
python -m spacy download en

Here is the example python code:

import spacy 

# Define a text string 
text = "This is a sample text. It contains some words that we can use for lemmatization." 

# Load the English language model in spaCy 
nlp = spacy.load('en') 

# Create a Doc object 
doc = nlp(text) 

# Lemmatize each token and print the result 
for token in doc: 
  lemma = token.lemma_ 
  print(token.text, "-->", lemma)

In this example, the lemma_ property of each token in the spaCy Doc object will contain the lemma of the word. For example, the word “contains” will be lemmatized to “contain,” and the word “words” will be lemmatized to “word.”

Gensim lemmatizer

You can also use the Gensim library for lemmatization in Python. Here is an example:

import gensim 
from gensim.utils import lemmatize 

# Define a text string 
text = "This is a sample text. It contains some words that we can use for lemmatization." 

# Use the lemmatize() function to lemmatize the text 
lemmas = lemmatize(text, stopwords=['is', 'it', 'we']) 

# Print the result 
print(lemmas)

Alternatives to lemmatization

Lemmatization has some limitations, such as its computational complexity and the need for an extensive vocabulary and morphological analysis of the words. Sometimes, these limitations make lemmatization impractical or unsuitable for your application.

If you are looking for alternative approaches to lemmatization, some common options include:

  • Stemming involves removing prefixes and suffixes from a word and sometimes even modifying its internal structure to reduce it to its root form. Stemming is a more straightforward and efficient method than lemmatization, but it often produces words that need to be validated or meaningful.
  • Synonym mapping involves replacing each word with a pre-defined synonym or set of synonyms. This can reduce the number of unique words in the text and make the text more consistent and easier to work with. However, it can also reduce the richness and diversity of the text and may only be suitable for some applications.
  • Dimensionality reduction: This involves using mathematical techniques, such as singular value decomposition (SVD) or non-negative matrix factorization (NMF), to reduce the number of dimensions in the text data. This can help identify the most important and relevant features in the text and make the data more manageable and efficient to work with. However, it can also lose some information and context in the process.

Ultimately, the approach chosen will depend on your application’s specific requirements and goals. Therefore, it may be necessary to experiment with different methods and techniques to find the best solution for your needs.

Key Takeaways

  • Lemmatization is one of the top 10 most useful NLP techniques for a reason. It’s helpful to reduce the dimensionality of your feature space before doing any machine learning. It’s, therefore, a vital part of many pre-processing pipelines.
  • Stemming is the main alternative to lemmatization. It yields less accurate results but is computationally faster. The main drawback of stemming is that it can sometimes create unmeaningful results, which makes further analysis impossible.
  • There are many practical use cases of lemmatization. It’s an essential step in text classification, sentiment analysis, topic modelling and information retrieval.
  • Python has some great libraries with lemmatization implementations. SpaCy, NLTK and Gensim are the main ones.
  • For some applications, lemmatization may be too slow. Alternatives to consider are stemming, synonym mapping and dimensionality reduction.

At Spot Intelligence we tend to use lemmatization in many of our pre-processing pipelines. However depending on the size of the data being processed this isn’t always a viable option and so we do use the alternatives as well. This just goes to show that there isn’t really a one size fits all solution in NLP but rather a variety of tools that are used in conjunction with one another.

What does a typical NLP pipeline look like for you? Do you use lemmatization or it’s alternatives? Let us know in the comments below.

Related Articles

Understanding Elman RNN — Uniqueness & How To Implement

by | Feb 1, 2023 | artificial intelligence,Machine Learning,Natural Language Processing | 0 Comments

What is the Elman neural network? Elman Neural Network is a recurrent neural network (RNN) designed to capture and store contextual information in a hidden layer. Jeff...

Self-attention Made Easy And How To Implement It

by | Jan 31, 2023 | Machine Learning,Natural Language Processing | 0 Comments

What is self-attention in deep learning? Self-attention is a type of attention mechanism used in deep learning models, also known as the self-attention mechanism. It...

Gated Recurrent Unit Explained & How They Compare [LSTM, RNN, CNN]

by | Jan 30, 2023 | artificial intelligence,Machine Learning,Natural Language Processing | 0 Comments

What is a Gated Recurrent Unit? A Gated Recurrent Unit (GRU) is a Recurrent Neural Network (RNN) architecture type. It is similar to a Long Short-Term Memory (LSTM)...

How To Use The Top 9 Most Useful Text Normalization Techniques (NLP)

by | Jan 25, 2023 | Data Science,Natural Language Processing | 0 Comments

Text normalization is a key step in natural language processing (NLP). It involves cleaning and preprocessing text data to make it consistent and usable for different...

How To Implement POS Tagging In NLP Using Python

by | Jan 24, 2023 | Data Science,Natural Language Processing | 0 Comments

Part-of-speech (POS) tagging is fundamental in natural language processing (NLP) and can be carried out in Python. It involves labelling words in a sentence with their...

How To Start Using Transformers In Natural Language Processing

by | Jan 23, 2023 | Machine Learning,Natural Language Processing | 0 Comments

Transformers Implementations in TensorFlow, PyTorch, Hugging Face and OpenAI's GPT-3 What are transformers in natural language processing? Natural language processing...

How To Implement Different Question-Answering Systems In NLP

by | Jan 20, 2023 | artificial intelligence,Data Science,Natural Language Processing | 0 Comments

Question answering (QA) is a field of natural language processing (NLP) and artificial intelligence (AI) that aims to develop systems that can understand and answer...

The Curse Of Variability And How To Overcome It

by | Jan 20, 2023 | Data Science,Machine Learning,Natural Language Processing | 0 Comments

What is the curse of variability? The curse of variability refers to the idea that as the variability of a dataset increases, the difficulty of finding a good model...

How To Implement A Siamese Network In NLP — Made Easy

by | Jan 19, 2023 | Machine Learning,Natural Language Processing | 0 Comments

What is a Siamese network? It is also commonly known as one or a few-shot learning. They are popular because less labelled data is required to train them. Siamese...

Top 6 Most Popular Text Clustering Algorithms And How They Work

by | Jan 17, 2023 | Data Science,Machine Learning,Natural Language Processing | 0 Comments

What exactly is text clustering? The process of grouping a collection of texts into clusters based on how similar their content is is known as text clustering. Text...

Opinion Mining — More Powerful Than Just Sentiment Analysis

by | Jan 17, 2023 | Data Science,Natural Language Processing | 0 Comments

Opinion mining is a field that is growing quickly. It uses natural language processing and text analysis to gather subjective information from sources. The main goal of...

How To Implement Document Clustering In Python

by | Jan 16, 2023 | Data Science,Machine Learning,Natural Language Processing | 0 Comments

Introduction to document clustering and its importance Grouping similar documents together in Python based on their content is called document clustering, also known as...

Local Sensitive Hashing — When And How To Get Started

by | Jan 16, 2023 | Machine Learning,Natural Language Processing | 0 Comments

What is local sensitive hashing? A technique for performing a rough nearest neighbour search in high-dimensional spaces is called local sensitive hashing (LSH). It...

How To Get Started With One Hot Encoding

by | Jan 12, 2023 | Data Science,Machine Learning,Natural Language Processing | 0 Comments

Categorical variables are variables that can take on one of a limited number of values. These variables are commonly found in datasets and can't be used directly in...

Different Attention Mechanism In NLP Made Easy

by | Jan 12, 2023 | artificial intelligence,Machine Learning,Natural Language Processing | 0 Comments

Numerous tasks in natural language processing (NLP) depend heavily on an attention mechanism. When the data is being processed, they allow the model to focus on only...

0 Comments

Submit a Comment

Your email address will not be published. Required fields are marked *