What is tokenization and lemmatization in NLP?


A subfield of artificial intelligence known as "natural language processing" (NLP) focuses on making computers capable of comprehending, interpreting, and producing human language. NLP assumes an essential part in different applications, including message examination, feeling examination, machine interpretation, question responding to frameworks, and that's just the beginning. In the domain of NLP, two basic strategies, to be specific tokenization and lemmatization, assume a crucial part in changing crude message into significant portrayals that can be additionally handled and dissected. We will go over these methods in detail, their significance, and how they help improve text analysis and comprehension in this article.

Tokenization and lemmatization in NLP


Tokenization is the method involved with separating a text record into more modest units called tokens. A token can be a word, a sentence, or even a person, contingent upon the granularity wanted. Tokenization is the vital initial phase in NLP, as it separates the crude text into reasonable units that can be broke down and handled.

Tokenization can be accomplished in a number of ways

  • Tokenization of Words − A document is broken up into individual words through a process known as word tokenization or word segmentation. Part-of-speech tagging, named entity recognition, and sentiment analysis are just a few examples of NLP applications that can benefit from this approach. The phrase "I love natural language processing," for instance, can be tokenized into the following phrases: I", "love", "normal", "language", "processing"].

  • Sentence Tokenization − A text is broken up into sentences using sentence tokenization. This method is essential for tasks like machine translation and summarization because it allows for sentence-level analysis. "Tokenization is the process of dividing a text document into smaller units," for instance, these units can be words, sentences, or characters. Two sentences can be tokenized as follows: The process of breaking up a text document into smaller pieces is known as tokenization. These units can be words, sentences, or characters."]

  • Tokenization of Characters − Character tokenization separates a text into individual characters. Character-level tokenization is not widely used, but it can be useful in certain situations, like analyzing spelling mistakes or dealing with languages where there are no clear word boundaries.

The benefits of tokenization include

  • Preprocessing of Text − By removing unnecessary characters, punctuation marks, and whitespace during tokenization, text data can be preprocessed to become cleaner and more structured.

  • Extraction of Features − With tokenization, meaningful features can be extracted from text and used as input for machine learning algorithms. Word frequencies, n-grams, and other linguistic attributes are examples of these features.

  • Visualization and Analysis of Text − Frequency analysis, topic modeling, and sentiment analysis are just a few of the text analysis methods that can be built on tokenization. Word clouds, word frequency distributions, and co-occurrence matrices are just a few of the visualizations that are made possible by it.


Lemmatization focuses on reducing text units to their base or root form, or lemma, whereas tokenization breaks text into individual units. The lemma eliminates variations caused by inflections or conjugations and represents the word's canonical form. Lemmatization improves the accuracy of subsequent NLP tasks, normalizes text, and reduces word complexity.

The following steps are involved in lemmatization

  • Tagging of Parts of Speech (POS) − Before lemmatization, every token is doled out a grammatical form tag (thing, action word, descriptor, and so on.) to disambiguate its significance. Due to the fact that words may take on various forms based on their usage and context, POS tagging aids in determining the correct lemma.

  • Query in Lexical Asset − A lexical resource, such as a lemmatization dictionary or morphological database, is used to determine a word's lemma. Taking into account the part-of-speech tags of the words, these resources contain mappings between them and their corresponding lemmas. Based on the information provided, the lookup process involves matching the token with its lemma.

  • The Lemmatization Method − In situations where an immediate query is unimaginable or the token is absent in the lexical asset, lemmatization calculations become possibly the most important factor. To return the word to its original form, these algorithms make use of linguistic rules and patterns. The WordNet lemmatizer, the Stanford lemmatizer, and the spaCy lemmatizer are examples of common algorithms.

The advantages of lemmatization are as follows

  • Normalization of Text −Lemmatization improves text normalization by reducing various word variations to a single base form. This interaction assists with disposing of repetitive portrayals and carries consistency to the information.

  • Jargon Decrease − Lemmatization lessens the jargon size by merging arched structures into their base structures. Reduced vocabulary sparsity can improve efficiency and accuracy in tasks like information retrieval and topic modeling, so this simplification is especially useful.

  • Improved Extraction of Features − Lemmatization makes it easier to find important characteristics in text data. By lessening words to their base structures, lemmatization considers a more exhaustive examination of word frequencies, n-grams, and semantic connections, bringing about more precise element portrayals.

Tokenization and Lemmatization in NLP Workflow

Tokenization and lemmatization are essential steps in the NLP workflow and frequently occur in succession. In various stages of NLP analysis, the utilization of these methods in combination provides numerous advantages −

  • Preprocessing − Tokenization allows for efficient preprocessing tasks like removing stop words, punctuation, and low-frequency words by breaking up text into smaller units. Lemmatization further improves this cycle by normalizing the leftover words to their base structures.

  • Representation of Text − Tokenization and lemmatization add to making significant message portrayals. The subsequent tokens and lemmas act as elements that can be utilized for additional examination, for example, building word embeddings, developing term-record grids, or producing word mists.

  • Data Recovery − Information retrieval systems rely heavily on tokenization and lemmatization. The systems are able to efficiently match user queries with relevant documents by tokenizing queries and documents and lemmatizing the tokens that are created as a result.

  • Analysis of Emotions − Lemmatization aids in capturing the sentiment-bearing essence of words, whereas tokenization makes it possible to extract individual words or phrases for sentiment analysis. By taking into account word variations and reducing noise, these methods make sentiment classification more accurate.

Challenges and Considerations

While tokenization and lemmatization are strong procedures in NLP, there are sure moves and contemplations to be aware of −

Ambiguity − A few words can have numerous implications relying upon the specific circumstance. Tokenization and lemmatization could battle to disambiguate such cases precisely, influencing downstream examination undertakings.

Out-of-Jargon (OOV) Words − Lemmatization and tokenization are based on lexical resources or dictionaries, which may not include all of a language's words. OOV words are difficult to analyze because they might not be properly tokenized or lemmatized, which could affect how accurate subsequent analyses are.

Dependencies on Language − Due to differences in word structure, morphology, and grammar, tokenization and lemmatization methods may differ between languages. When using these methods, it's critical to consider resources and rules specific to the language to guarantee accurate results.

Efficiency and Performance − Particularly for large datasets, tokenization and lemmatization can be computationally expensive. In real-time or resource-constrained environments, efficient processing necessitates careful implementation and optimization strategies.

Propagation of Errors − Botches made during tokenization or lemmatization can engender through downstream examination undertakings, prompting incorrect outcomes. As a result, the quality of tokenization and lemmatization outputs must be evaluated and validated with care.


In conclusion, To effectively analyze and comprehend text data, NLP heavily relies on tokenization and lemmatization. Word normalization and language comprehension are aided by lemmatization, which strips words down to their fundamental forms. To facilitate further analysis, tokenization breaks down raw text into smaller units. Text preprocessing, feature extraction, sentiment analysis, machine translation, and other NLP tasks all benefit from these techniques. NLP practitioners are given the ability to extract useful insights from textual data by making use of tokenization and lemmatization. This improves the accuracy, efficiency, and language processing capabilities of NLP systems.

Updated on: 13-Jul-2023


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