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Prerita Agarwal

Data Specialist @

23 Jul, 2024 @ 01:30 PM

Introduction

Data mining is a process that involves exploring large datasets to uncover hidden patterns, unknown correlations, and other useful information. Among the various techniques used, partitioning methods play a crucial role in the clustering of data. Clustering is a technique used to group similar data points together. In this article, we'll explore the specifics of partitioning methods, focusing on K-Means and K-Medoids, two popular clustering techniques.

By the end of this read, you'll have a clear understanding of how these methods work, their differences, applications, and which one might be more robust for your data mining needs.

K-Means (A Centroid-Based Technique)

K-Means is one of the simplest and most commonly used clustering methods in data mining. It's a centroid-based technique, meaning it groups data points around a central point, known as a centroid. This method is particularly useful in segmenting a dataset into distinct, non-overlapping subsets or clusters.

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How does K-Means Work?

K-Means clustering works by partitioning a dataset into K distinct, non-overlapping subgroups, where each data point belongs to only one group. The process is straightforward:

Initialize Centroids:

Randomly pick K points as the initial centroids.

Assign Data Points:

Assign each data point to the nearest centroid, forming K clusters.

Update Centroids:

Recalculate the centroid of each cluster.

Iterate:

Repeat the assigning and updating steps until the centroids no longer change significantly.

This iterative process continues until the centroids stabilize, ensuring that the data points within each cluster are as close as possible to their respective centroid.

Algorithm

Let's delve into a basic implementation of the K-Means algorithm in Python:

Install Necessary Libraries

pip install numpy matplotlib sklearn

Import Libraries & Prepare Data

import numpy as np
import matplotlib.pyplot as plt
from sklearn.cluster import KMeans
from sklearn.datasets import make_blobs
# Generate synthetic data for demonstration
dataset, _ = make_blobs(n_samples=300, centers=4, cluster_std=0.60, random_state=0)

In this example, we use a synthetic dataset for simplicity. The make_blobs function generates a dataset suitable for clustering. We then apply the K-Means algorithm and visualize the clusters and their centroids.

What are K-Medoids?

K-Medoids is a clustering algorithm similar to K-Means, but with a key difference in how the centers of clusters are determined. In K-Medoids, the center of each cluster, known as a medoid, is an actual data point from the dataset. This makes K-Medoids particularly effective in scenarios where centroids (mean of points) are not representative due to outliers or non-numeric data.

Key Characteristics of K-Medoids

Medoids: It uses actual data points as the central elements of clusters.

Robustness to Outliers: More resistant to outliers compared to K-Means.

Suitability for Non-Numeric Data: Efficient for clustering non-numeric data where mean or median cannot be defined.

Practical Example of K-Medoids

Imagine you're running a delivery service and want to optimize the location of your delivery hubs. You have a dataset of delivery addresses, and you need to cluster them to find the best locations for your hubs. K-Medoids is ideal for this, as it will pinpoint actual delivery addresses as potential hub locations.

Implementing K-Medoids in Python

Let's implement K-Medoids using Python. We'll use a synthetic dataset for clarity.

Install the Necessary Library

pip install scikit-learn-extra

Import Libraries & Prepare Data

import numpy as np
from sklearn_extra.cluster import KMedoids
import matplotlib.pyplot as plt
# Generating a synthetic dataset
X = np.array([[1, 2], [2, 2], [1, 4],
[4, 4], [4, 3], [5, 5]])

In this example, we've clustered the dataset into two groups and marked the medoids. K-Medoids has chosen actual data points as the central elements of these clusters, which is particularly useful in real-world scenarios like our delivery service example.

K-Medoids is a versatile and robust clustering technique that excels in specific situations where K-Means might not be the best fit, especially in the presence of outliers or for categorical data clustering. Its application is widespread, from business analytics to bioinformatics, offering a reliable alternative to centroid-based clustering methods.

Difference Between K-Means & K-Medoids Clustering

Understanding the differences between K-Means and K-Medoids is crucial for selecting the right method for your data mining tasks. Letâ€™s compare these two popular clustering techniques:

Cluster Centers

K-Means: Uses the mean (average) of the data points in a cluster to define its center (centroid).

K-Medoids: Chooses actual data points as the center (medoids) of the clusters.

Sensitivity to Outliers

K-Means is sensitive to outliers since the mean can be skewed by extreme values.

K-Medoids is more robust to outliers, as medoids are less likely to be outliers themselves.

Use Cases

K-Means is preferred for larger datasets and where computation speed is a priority. It works well with numerical data where calculating the mean is meaningful.

K-Medoids is more suited for smaller datasets or when the dataset contains outliers or categorical data.

Algorithmic Complexity

K-Means is generally faster and more computationally efficient, making it scalable to large datasets.

K-Medoids can be computationally more expensive, especially as the size of the dataset increases.

Which is More Robust - K-Means or K-Medoids?

In terms of robustness, especially when dealing with outliers or non-numerical data, K-Medoids generally holds the upper hand. Its method of using actual data points as cluster centers provides a more accurate representation in these scenarios. However, this doesn't mean K-Means is inferior; it's simply more suitable for different types of datasets and objectives.

Applications of Clustering

Both K-Means and K-Medoids are used in various fields:

Market Segmentation

Businesses use these techniques for customer segmentation based on buying behavior or preferences.

Image Processing

For segmenting digital images into meaningful clusters, making it easier to analyze and interpret them.

Bioinformatics

Clustering genetic data to find patterns or relationships among different species or genes.

Document Clustering: Used in text mining to group similar documents for information retrieval or organization.

Frequently Asked Questions

What is partition method in data mining?

Partitioning methods in data mining is a popular family of clustering algorithms that partition a dataset into K distinct clusters. These algorithms aim to group similar data points together while maximizing the differences between the clusters.

What is the random partition method?

In random partitioning, records are randomly distributed across all processing nodes. Like round robin, random partitioning can rebalance the partitions of an input data set to guarantee that each processing node receives an approximately equal-sized part of the data.

What makes K-Medoids more suitable for handling outliers than K-Means?

K-Medoids is more robust to outliers because it uses actual data points as the centers of clusters (medoids), which are less likely to be influenced by extreme values. In contrast, K-Means uses the mean of the cluster's points as the center, which can be significantly skewed by outliers.

Conclusion

In summary, K-Means and K-Medoids are powerful clustering techniques in data mining, each with its strengths and ideal use cases. K-Means excels in computational efficiency and is well-suited for large datasets with numerical data, while K-Medoids offers robustness against outliers and applicability to non-numerical data. Understanding these methods' workings, differences, and applications enables more effective and tailored data analysis strategies.