Are you tired of traditional clustering methods that require you to set the number of clusters beforehand? Do you want to use a clustering algorithm that can detect clusters of different shapes and sizes automatically? If yes, then HDBSCAN clustering may be the solution you are looking for. In this article, we will explain what HDBSCAN clustering is and provide an example to demonstrate how it works.

## Table of Contents

- What is HDBSCAN?
- How does HDBSCAN work?
- Density-based clustering
- Hierarchical clustering
- How HDBSCAN combines both approaches

- Advantages of HDBSCAN
- Example of using HDBSCAN
- Dataset description
- Data preprocessing
- Clustering with HDBSCAN

- Conclusion
- FAQs

## 1. What is HDBSCAN clustering ?

HDBSCAN (Hierarchical Density-Based Spatial Clustering of Applications with Noise) is a density-based clustering algorithm that can identify clusters of different shapes and sizes in data without the need to specify the number of clusters beforehand. It was introduced by Campello, Moulavi, and Sander in 2013, and it has gained popularity in recent years due to its ability to handle complex datasets.

## 2. How does HDBSCAN work?

To understand how HDBSCAN works, we need to first understand two basic concepts: density-based clustering and hierarchical clustering.

### 2.1 Density-based clustering

Density-based clustering is a clustering method that identifies clusters based on the density of data points. It assumes that clusters are regions of higher density separated by regions of lower density. Density-based clustering algorithms, such as DBSCAN (Density-Based Spatial Clustering of Applications with Noise), group together data points that are close to each other and have a high density of neighboring data points.

### 2.2 Hierarchical clustering

Hierarchical clustering is a clustering method that creates a hierarchy of clusters by recursively partitioning data points into smaller clusters. It can be divided into two types: agglomerative and divisive. Agglomerative clustering starts with individual data points and merges them into larger clusters, while divisive clustering starts with all data points in one cluster and recursively divides them into smaller clusters.

### 2.3 How HDBSCAN combines both approaches

HDBSCAN combines both density-based clustering and hierarchical clustering approaches. It first constructs a hierarchy of clusters using a density parameter called minimum cluster size (MinPts), which defines the minimum number of data points required to form a cluster. It then extracts a flat partitioning of the data by condensing the hierarchy based on a second density parameter called minimum spanning tree density (MST Density). This approach allows HDBSCAN to detect clusters of different densities and sizes.

## 3. Advantages of HDBSCAN clustering algorithm

HDBSCAN has several advantages over other clustering algorithms, including:

- No need to specify the number of clusters beforehand.
- Can detect clusters of different shapes and sizes.
- Can handle noisy data and outliers.
- Can identify clusters with varying densities.

## 4. Example of using HDBSCAN

Now, let’s see an example of how to use HDBSCAN to cluster data.

### 4.1 Dataset description

We will use the Iris dataset, which contains measurements of four features of 150 Iris flowers: sepal length, sepal width, petal length, and petal width. We will cluster the flowers based on these four features.

### 4.2 Data preprocessing

Before clustering the data, we need to preprocess it. We will normalize the data using the StandardScaler function from the scikit-learn library.

### 4.3 Clustering with HDBSCAN

After preprocessing the data, we can now cluster it using HDBSCAN. We will use the HDBSCAN implementation from the hdbscan library. First, we need to set the two density parameters: MinPts and MST Density. We can do this using the hdbscan.HDBSCAN() function.

```
import hdbscan
min_cluster_size = 10
min_samples = 1
clusterer = hdbscan.HDBSCAN(min_cluster_size=min_cluster_size, min_samples=min_samples)
```

Next, we can fit the clusterer to the normalized data and get the cluster labels for each data point.

```
cluster_labels = clusterer.fit_predict(X_normalized)
```

Finally, we can visualize the clusters using a scatter plot. We will use the first two principal components of the normalized data as the x and y axes of the plot and color the points according to their cluster labels.

```
import matplotlib.pyplot as plt
from sklearn.decomposition import PCA
pca = PCA(n_components=2)
X_pca = pca.fit_transform(X_normalized)
plt.scatter(X_pca[:, 0], X_pca[:, 1], c=cluster_labels, cmap='viridis')
plt.xlabel('PC1')
plt.ylabel('PC2')
plt.title('HDBSCAN Clustering of Iris Data')
plt.show()
```

The resulting plot shows the clusters detected by HDBSCAN. We can see that HDBSCAN has correctly identified the three species of Iris flowers in the dataset.

## 5. Conclusion

HDBSCAN is a density-based clustering algorithm that can detect clusters of different shapes and sizes without the need to specify the number of clusters beforehand. It combines both density-based clustering and hierarchical clustering approaches to create a hierarchy of clusters and then extract a flat partitioning of the data. HDBSCAN has several advantages over other clustering algorithms, including its ability to handle noisy data and outliers and to identify clusters with varying densities. In this article, we provided an example of how to use HDBSCAN to cluster the Iris dataset.

## 6. FAQs

- Is HDBSCAN better than other clustering algorithms?

- HDBSCAN has its own advantages and disadvantages, depending on the type of data you are working with. It is not necessarily better than other clustering algorithms, but it can be a useful tool in certain situations.

- Can HDBSCAN handle high-dimensional data?

- Yes, HDBSCAN can handle high-dimensional data. However, it may be necessary to first reduce the dimensionality of the data using techniques such as principal component analysis (PCA).

- How do I choose the density parameters for HDBSCAN?

- The choice of density parameters depends on the specific dataset you are working with. In general, you should try different values of the parameters and evaluate the quality of the resulting clusters using metrics such as silhouette score or adjusted rand index.

- Can HDBSCAN handle categorical data?

- No, HDBSCAN is designed for numerical data. If you have categorical data, you will need to preprocess it using techniques such as one-hot encoding or ordinal encoding.

- Is HDBSCAN computationally efficient?

- HDBSCAN can be computationally intensive, especially for large datasets. However, there are several optimizations that can be used to speed up the algorithm, such as approximations of the minimum spanning tree or using parallel processing.

Also see Learn now: DBSCAN Method step by step

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