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What is Text Clustering?

Venessa Fabio
Venessa Fabio
Feb 2, 2023
3 min read


In today's technology-driven society, the constant influx of information in the form of emails, presentations, and academic papers can pose a significant challenge, especially for students with vast amounts of reading material to digest and comprehend. But what if there was a more efficient way to handle all that text?

Text Clustering, an NLP technique, offers a solution. By grouping similar documents or sentences based on their content&meaning, it facilitates efficient categorization and analysis of large volumes of information. No more endless scrolling through pages of text to understand its essence. Instead, you can focus on the most relevant information, saving time in the process.

In this article, we'll delve into the intricacies of Text Clustering and demonstrate how it can revolutionize the way you interact with the text. You'll learn how it can transform the way you study and work with text, providing a well-structured symphony of information instead of overwhelming information overload. Get ready to discover the potential of Text Clustering.


Understanding Text Clustering

Definition of text clustering

It is a subfield of Natural Language Processing (NLP) that involves grouping similar documents or sentences based on their content. It is a method of organizing large amounts of textual information into meaningful categories or clusters, providing a high-level overview of the information contained within.

Imagine a library where all the books are thrown together in a heap. How would you find the book you're looking for? Text Clustering is like having a librarian who can categorize all the books for you. No more wandering aimlessly through the stacks, trying to find what you're looking for.

NLP text clustering

Types of Clustering

Let's use the familiar example of a library and books to explain the various types of Text Clustering. So, we are in a library, filled with books of all genres, topics, and sizes. Clustering is like organizing these books into categories, so you can easily find what you're looking for. Text clustering works the same way, but instead of books, it's dealing with words and sentences. And just like there are different ways to categorize books, there are different ways to cluster text.

Flat or hierarchical 

Flat Clustering: Imagine a librarian organizing books into fixed sections of the library, like "Mystery," "Science Fiction," and "Romance." That's flat clustering. It's simple and straightforward, but it might not capture the complexity of book relationships.

types of text clustering
Flat Clustering

Hierarchical Clustering: This is like building a tree of books, where larger branches are divided into smaller branches, and so on until you reach the leaves. Hierarchical clustering allows for more nuanced categorization of the text, capturing the complex relationships between words and sentences.

hierarchical text clustering
Hierarchical Clustering

There are two sub-types of Hierarchical Clustering: Agglomerative and Divisive. Agglomerative starts with individual text documents as leaves and then merges them into larger branches. Divisiveness starts with all the text documents grouped together and then splits them into smaller branches. Both methods ultimately aim to build a hierarchy of clusters, capturing the complex relationships between words and sentences.

Based on overlaps

Soft Clustering: Imagine a library that has a section for "Cooking" books. The librarian comes across a book about "Vegetarian Cooking" and another about "Gluten-Free Cooking." They might categorize the first book under "Cooking" and the second book under "Cooking" and "Health," as both sections are relevant to the book's content. This is an example of soft clustering, where a book can belong to multiple sections of the library, depending on its relevance.

Hard Clustering: This one is like the strict librarian who only allows books to belong to one section of the library at a time. Hard clustering is rigid and straightforward, assigning each text document to a single cluster.

Hard Clustering vs Soft Clustering
Hard Clustering vs Soft Clustering

Based on Goals

Monothetic Clustering: Imagine a librarian organizing books based on one specific feature, like the author's name. That's monothetic clustering. It's a form of hierarchical clustering that focuses on one attribute or feature of the text.

Polythetic Clustering: This is like a librarian organizing books based on multiple features, like the author's name, genre, and publication date. Polythetic clustering considers multiple attributes or features of the text, leading to more diverse and nuanced categorization.

So, there you have it. Different ways to categorize the vast collection of words and sentences, just like organizing a library filled with books.

Levels of Clustering

Clustering levels can be seen as the different elevations at which we categorize and group our data. These levels determine the granularity of the clusters and allow us to see our information from different perspectives. Let's take a closer look:

Document Level Clustering: This level takes us to the mountaintop, where we have a panoramic view of our documents. Here, we group our data based on common themes, topics, or subjects, like news articles, emails, search engine results, etc.

Sentence Level Clustering: This level takes us a little lower, where we can see our data in finer detail. We use this level to cluster sentences that belong to different documents. For example, this type of clustering is used in the analysis of tweets, where we group tweets based on common topics or sentiments.

Word Level Clustering: This level brings us down to the ground, where we can see our data in its rawest form. We group words based on their themes, topics, or meanings. For example, by collecting synonyms for a particular word, we can form a cluster of words. This level is often used in lexical databases like WordNet, which groups English words into sets of synonyms called synsets.

Key concepts used in Text Clustering

Here are the fundamental building blocks of Text Clustering aka key concepts, that will help to move further in the understanding of this process:

Distance Measure: Think of this as a yardstick that measures how similar or different two documents are. The most commonly used distance measures for Text Clustering are Cosine Similarity and Euclidean Distance.

Criterion Function: This is like a compass that guides the clustering process. It helps determine when the best possible clustering has been achieved, and it's time to stop processing. The most commonly used criterion functions are Calinski-Harabasz and Davies-Bouldin.

Algorithms: These are the engines that power the Text Clustering process. The two most commonly used algorithms are K-Means and Hierarchical Clustering. K-Means works by iteratively refining clusters, while Hierarchical Clustering builds a tree of clusters, starting with the largest branches and ending with the smallest leaves.

Feature Extraction: This is like a translator that helps the clustering process understand the text data. It transforms text documents into numerical vectors, making it easier for distance measures and algorithms to work with them. The most commonly used feature extraction techniques are Term Frequency-Inverse Document Frequency (TF-IDF) and Latent Dirichlet Allocation (LDA).

How does it work?

The text clustering process involves several stages of data preprocessing, feature extraction, and similarity measurement. The goal of these stages is to transform raw text data into numerical representations that can be processed and analyzed by machine learning algorithms.

The process stages

Preprocessing: The first step in text clustering is to preprocess the text data. This includes cleaning and prepping the data to make it suitable for analysis. This can involve removing unwanted characters, converting all text to lowercase, removing stop words, stemming and lemmatizing words, and transforming the data into a numerical representation, such as a term frequency-inverse document frequency (TF-IDF) matrix.

Feature extraction: The next step is to extract features from the text data that can be used to calculate the similarity between documents. This can involve calculating word frequencies, creating word embeddings, or using term frequency-inverse document frequency (TF-IDF) values.

Similarity measure: Once features have been extracted, a similarity measure is used to determine the similarity between pairs of documents. This can involve calculating the Euclidean distance, Cosine similarity, or Jaccard similarity between documents.

Clustering algorithm: The next step is to apply a clustering algorithm to group the documents into clusters. Popular algorithms include k-means, hierarchical clustering, and DBSCAN. The choice of algorithm will depend on the nature of the data, the desired number of clusters, and the computational resources available.

Evaluating the clusters: Finally, the clusters are evaluated to assess the quality of the clustering. This can involve using internal evaluation metrics, such as the silhouette score or the Calinski-Harabasz index, or external evaluation metrics, such as ground truth labels or manual inspection.

Text Clustering algorithms

Selecting the appropriate algorithm is a crucial aspect of clustering that greatly influences the outcome. So, once the data has been preprocessed and transformed, a clustering algorithm is applied to the data to group similar documents together into clusters. Let's take a closer look at some of the most widely used algorithms:

K-Means Clustering is an iterative algorithm that groups data points into K clusters. The algorithm starts by selecting K centroids randomly and updates them by computing the mean of the data points closest to each centroid. This process is repeated until the centroids stop moving or reach a stopping criterion.

Fuzzy C-Means is an extension of K-Means that allows a data point to belong to multiple clusters, with a degree of membership. The algorithm uses a membership matrix to represent the fuzzy cluster assignment.

Gaussian Mixture Model is a probabilistic algorithm that models data as a mixture of several Gaussian distributions, each representing a cluster. The algorithm estimates the parameters of the Gaussian distributions and the mixture weights to optimize the likelihood of the data.

Spectral Clustering is a clustering algorithm that uses the eigenvectors of a similarity matrix to perform clustering. The similarity matrix captures the relationships between data points and is often derived from a graph Laplacian.

Affinity Propagation is a clustering algorithm that uses message passing between data points to allow points to choose their own cluster representatives. The algorithm estimates the cluster representatives and the cluster assignments that maximize the "responsibility" and "availability" matrices.

Meanshift Clustering is a non-parametric algorithm that iteratively shifts points to the mode of the density of points in their vicinity, eventually converging to the clusters. The algorithm does not require the number of clusters to be specified beforehand.

Hierarchical Agglomerative Clustering is a hierarchical clustering algorithm that starts with each data point as a separate cluster and iteratively merges small clusters into larger ones until all data points are grouped together. The algorithm produces a dendrogram that shows the hierarchical relationships between clusters.

The table below indicates which algorithms are typically used for specific types of clustering:

Algorithms classifications
Algorithms classifications


There are several challenges in text clustering that are currently attracting significant attention in the field. These challenges include:

High dimensionality: Text data is often highly dimensional, making it difficult to perform clustering efficiently. This requires the use of dimensionality reduction techniques or other methods to address the issue.

Heterogeneity: Text data can be very diverse in nature, making it challenging to find meaningful clusters. This requires the use of more sophisticated clustering algorithms or additional preprocessing steps to account for the heterogeneity.

Scalability: With the increasing amount of text data being generated, scalability is a major challenge in text clustering. This requires the use of parallel or distributed computing techniques to perform clustering on large datasets.

Handling noisy data: Text data can be noisy, with errors, typos, or irrelevant information that can negatively impact clustering results. This requires the use of techniques to clean the data or methods to handle noisy data in the clustering process.

These challenges have arisen due to the increasing availability of large text datasets, the increasing complexity of text data, and the growing demand for more sophisticated text clustering techniques. The goal is to develop more effective methods for performing text clustering and to tackle these challenges in order to generate more useful and accurate results.

Use cases of Text Clustering

The potential for text clustering is vast and it has a wide range of applications. By grouping similar texts together, businesses can effectively categorize and analyze large amounts of information, allowing for more efficient and effective decision-making. Text clustering can be utilized in fields such as marketing, customer service, and information retrieval, among others, to uncover hidden insights and trends, improve customer satisfaction, and streamline information management processes. With its ability to process vast amounts of unstructured data, text clustering has become a valuable tool for businesses looking to stay ahead of the curve. Below are the most interesting examples:

Fake News Identification: The study by Kasra Majbouri, et al. applied K-Means clustering to detect fake news by clustering news articles into real and fake based on the words in the articles. The process involved computing the similarity between features, clustering features, reducing the dataset, and detecting fake news with an accuracy of 87%. This highlights the potential of text clustering in identifying false information.

Topic Modeling: Another interesting application of text clustering is topic modeling, which involves grouping texts based on the topics they cover. This can be useful for news articles, scientific papers, or customer queries, allowing for effective categorization and analysis of large amounts of information.

Sentiment Analysis: One of the most popular applications of text clustering is sentiment analysis. This involves grouping texts based on their emotional tone, such as positive, negative, or neutral. Sentiment analysis can be applied to customer feedback, product reviews, or social media posts to gain insights into customer opinions and preferences.                                                                                                                            

How to try Text Clustering?

With a solid understanding of text clustering in place, it's time to put the theory into practice. One practical approach to getting started with clustering is to use a product-ready NLP-as-a-Service platform. This will not only save time and effort but also provide a fast and easy way to start clustering and getting results. 

OneAI is exactly such a platform with use case-ready API and no-code Language Studio where it’s possible to immediately try clustering, as well as many other Language Skills, like sentiment analysis or highlights detection.

Visit the Studio to interact and see a live example of airline customer service tickets. This example uses clustering by clients’ voices aka requests. The biggest plate represents the title of the most popular clients’ voices united by meaning, on the screenshot below it’s “speak to agent”.

One AI studio speak to agent
OneAI studio speak to agent

By clicking on the title, we will see specific phrases that customers used on the topic, grouped by frequency of use. 

One AI studio speak to representative
OneAI studio speak to representative

You can click through other examples to get a full idea of how it works. In case of any questions, please schedule a demo or try our Language Studio by yourself. 


As we've seen, text clustering is like a secret weapon in the arsenal of data analysis tools. Its ability to quickly categorize vast amounts of text data into meaningful groups is not just useful, but essential in today's world where information overload is the norm. The next time you're faced with a big pile of text data, remember the power of text clustering and unleash its potential to uncover insights and make data-driven decisions like a pro.

Unlock Text Clustering's Potential Today!


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