Classification in Machine Learning: Understanding the Basics and Best Practices

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Updated October 15, 2023

Classification in Machine Learning

In machine learning, classification is the task of assigning a label or category to a piece of data based on its features. This process involves training a machine learning algorithm on a labeled dataset, where the labels correspond to the correct class or category for each example. The goal of classification is to learn a model that can accurately predict the label for new, unseen data.

Types of Classification

There are several types of classification, including:

Binary Classification

Binary classification involves assigning a label to an example based on two possible classes or categories. For example, spam vs. not spam emails, or cancer vs. non-cancer medical diagnoses.

Multi-Class Classification

Multi-class classification involves assigning a label to an example based on more than two possible classes or categories. For example, handwritten digit recognition (e.g. 0-9) or product categorization (e.g. electronics, clothing, etc.).

Multi-Label Classification

Multi-label classification involves assigning multiple labels to an example based on several categories. For example, image tagging with multiple keywords or labels.

Hierarchical Classification

Hierarchical classification involves organizing classes into a hierarchy, where more general classes are the parent class of more specific child classes. For example, animal species can be organized into a hierarchy based on kingdom, phylum, class, order, family, genus, and species.

How Classification Works

The process of classification typically involves the following steps:

Data Collection

Gathering a dataset of labeled examples, where each example is associated with a label or category.

Data Preprocessing

Cleaning and preprocessing the data to ensure it is in a format that can be used by the machine learning algorithm. This may involve removing missing values, handling outliers, and transforming features.

Model Selection

Choosing an appropriate machine learning algorithm for the classification task based on factors such as the size of the dataset, the complexity of the problem, and the available computational resources.


Training the selected algorithm on the labeled dataset to learn the relationships between the features and the labels.


Evaluating the performance of the trained model on a separate test set to assess its accuracy and suitability for the task at hand.


Deploying the trained model in a production environment, where it can be used to make predictions on new, unseen data.

Common Techniques Used in Classification

Several techniques are commonly used in classification, including:

Decision Trees

Decision trees involve partitioning the feature space into regions based on the values of the features. Each internal node in the tree represents a feature selection and a split in the data.

Random Forests

Random forests involve training multiple decision trees on random subsets of the data and combining their predictions to produce the final output. This can help improve the accuracy and reduce overfitting compared to a single decision tree.

Support Vector Machines (SVMs)

SVMs involve finding the hyperplane that maximally separates the classes in the feature space. SVMs can be used for both binary and multi-class classification.

Neural Networks

Neural networks are a class of machine learning models that are particularly well-suited to classification tasks. They can learn complex relationships between the features and the labels, and can handle large datasets.

Challenges in Classification

Classification can be challenging due to several reasons, including:


Overfitting occurs when a model is too complex and learns the noise in the training data, rather than the underlying patterns. This can result in poor generalization performance on new, unseen data.

Imbalanced Datasets

Imbalanced datasets occur when one class has a significantly larger number of examples than the other classes. This can affect the accuracy of the model, as the model may be biased towards the majority class.

High-Dimensional Feature Spaces

High-dimensional feature spaces can make it difficult to identify the most relevant features and avoid overfitting.


Classification is a fundamental task in machine learning that involves assigning a label or category to an example based on its features. There are several types of classification, including binary, multi-class, multi-label, and hierarchical classification. The process of classification typically involves data collection, data preprocessing, model selection, training, evaluation, and deployment. Common techniques used in classification include decision trees, random forests, support vector machines (SVMs), and neural networks. Classification can be challenging due to overfitting, imbalanced datasets, and high-dimensional feature spaces.