Data Science

A Brief Introduction to Unsupervised Learning Algorithms

Published: 12th June, 2023

Harshini Bhat

Data Science Consultant at almaBetter

Discover the basics of unsupervised learning algorithms and its importance in data analysis. Learn about clustering, dimensionality reduction, and use cases.

Are you familiar with the term "unsupervised learning"? It's a fascinating field of machine learning that involves training algorithms to find patterns and relationships within data without any predefined labels or categories. That's right - these unsupervised learning algorithms are left to their own devices to discover the underlying structure of the data on their own.

Unsupervised learning algorithms, also known as unsupervised machine learning algorithms, are a crucial part of the machine learning ecosystem. They have numerous applications in fields such as marketing, finance, healthcare, and more.

Let us dive deep into techniques of unsupervised learning and explore the basics of how it works, the different types of algorithms used, and some common use cases. So, get ready to learn about unsupervised learning in machine learning!

Definition of Unsupervised Learning:

Unsupervised learning is a type of machine learning that involves training an algorithm to find patterns and relationships within data without any predefined labels or categories. This means that the algorithm must identify the underlying structure of the data and group similar data points together based on their similarities.

Unlike supervised learning, where the algorithm is given a labeled dataset to learn from, unsupervised learning algorithms are left to discover the underlying structure of the data on their own. This makes unsupervised learning particularly useful in situations where labeled data is scarce or difficult to obtain.

Basics of Unsupervised Learning:

Differences between unsupervised and supervised learning:

Supervised LearningUnsupervised Learning
Input data is labeled with an output variable.


Input data is unlabeled.

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Algorithm learns to predict an output variable based on input variables.


Algorithm learns to discover the underlying structure of the data.

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Requires a large amount of labelled data for training.


Requires a large amount of unlabeled data for training.

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Performance is measured by comparing predicted outputs to actual outputs.


Performance is measured by how well the algorithm discovers the structure of the data.

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Common algorithms include regression, classification, and neural networks.


Common algorithms include clustering, dimensionality reduction, and generative models.

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Examples of applications include image recognition, speech recognition, and sentiment analysis.


Examples of applications include anomaly detection, customer segmentation, and pattern recognition.


Working of Unsupervised Learning


Working of Unsupervised Learning

In unsupervised learning, the input data that is given is not categorized, and corresponding outputs are not given. The machine learning model is fed the unlabeled input data to find hidden patterns and relationships within the data. After interpreting the raw data, the model applies suitable algorithms such as k-means clustering, decision trees, or other techniques.

Once the algorithm is applied, it groups the data objects into clusters based on their similarities and differences. This process allows the model to identify patterns and find relationships within the data, which can also be used in different applications, such as customer segmentation or anomaly detection.

Techniques used in unsupervised learning:

  • Clustering algorithms group similar data points together based on their similarities, which can help identify patterns and relationships within the data.
  • Dimensionality reduction algorithms reduce the number of variables in a dataset while still retaining as much of the original information as possible, which helps to simplify the given data and make it easier to analyze.
  • Generative models generate synthetic data based on the patterns and relationships found in the original dataset, which can also be used to increase the size of the dataset and improve the performance of supervised learning algorithms.

Types of Unsupervised Learning Algorithm:

There are two main types of unsupervised learning algorithms: clustering and association.


Types of unsupervised Learning Algorithms


Clustering is a method of grouping similar data points together. In clustering, the machine learning model tries to find similarities between data points based on their features. The goal is to create groups or clusters of data points that are similar to one another and dissimilar to data points in other clusters. Clustering is used in various applications, such as customer segmentation, image recognition, and anomaly detection.

One popular clustering algorithm is k-means clustering, which aims to partition a dataset into k clusters based on their similarities. The algorithm works by randomly assigning initial cluster centroids, then iteratively adjusting the centroids until the clusters are optimized. Another clustering algorithm is hierarchical clustering, which creates a tree-like diagram that shows the relationship between clusters.

For example, in customer segmentation, clustering can be used to group customers based on their demographic information, purchasing history, or behavior on a website. This information can be then used to tailor marketing campaigns or personalize customer experiences.


Association rules are used to identify patterns and relationships between variables in a dataset. The goal is to determine which items tend to occur together in the dataset. Association rules are commonly used in market basket analysis to identify which products are frequently purchased together.

One popular algorithm for association rules is the Apriori algorithm, which is based on the idea that if an itemset is frequent, then all its subsets must also be frequent. This algorithm generates a set of candidate itemsets, then prunes them based on their support and confidence.

For example, in market basket analysis, association rules are used to identify which products are frequently purchased together. If a retailer observes that many customers who purchase bread also purchase butter or jam, they can use this information to bundle the products together or offer targeted promotions.

Unsupervised Learning algorithms:

Some of the most popular unsupervised learning algorithms:

  • K-means clustering
  • KNN(k-nearest neighbors)
  • Hierarchal clustering
  • Anomaly detection
  • Neural Networks
  • Principle Component Analysis
  • Independent Component Analysis
  • Apriori algorithm
  • Singular value decomposition

Advantages and Disadvantages

Advantages of Unsupervised Learning:

  • Unsupervised learning can be used for more complex tasks as compared to supervised learning because we don't require labeled input data.
  • Unsupervised learning is preferable as it is easier to obtain unlabeled data in comparison to labeled data, which sometimes can be costly and time-consuming to collect.

Disadvantages of Unsupervised Learning:

  • Unsupervised learning is inherently more difficult than supervised learning since we don't have corresponding output to compare with.
  • The result of unsupervised learning algorithms might be less accurate than supervised learning algorithms since the input data is not labeled, and the algorithms don't have a predetermined output to optimize towards.

Common Use Cases of Unsupervised Learning

Unsupervised learning has a wide range of use cases across industries. Some common use cases include:

  • Market segmentation for targeted marketing campaigns: Unsupervised Learning is also used to group customers into segments based on similarities in their purchasing behavior or demographics, allowing companies to tailor their marketing strategies to specific groups.


  • Fraud detection for identifying anomalies in financial data: Unsupervised learning is also used to detect anomalies in financial data, which can help identify potential fraud.


Anomoly Detection

  • Natural Language Processing (NLP) for document classification and sentiment analysis: Unsupervised learning can be used for tasks like document classification and sentiment analysis, where we want to group similar documents or analyze the sentiment of a piece of text without pre-defined labels.




Unsupervised Learning is a powerful tool in machine learning that can help extract insights from unlabeled data. By finding hidden patterns and relationships in the data, unsupervised learning algorithms like clustering and dimensionality reduction can help solve complex problems across industries, from targeted marketing to fraud detection. While unsupervised learning does have its disadvantages, such as the lack of predetermined output to compare with, its advantages, like the ability to work with unlabeled data, make it a valuable technique in data analysis. As businesses and researchers continue to generate vast amounts of unlabeled data, the importance of unsupervised learning in machine learning is only set to increase.

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