## Introduction to Clustering Methods

Clustering methods (like Hierarchical method, Partitioning, Density-based method, Model-based clustering, and Grid-based model) help in grouping the data points into clusters, using the different techniques are used to pick the appropriate result for the problem, these clustering techniques helps in grouping the data points into similar categories and each of these subcategories is further divided into subcategories to assist the exploration of the queries output.

### Explain Clustering Methods?

This clustering method helps in grouping valuable data into clusters and from that picks appropriate results based on different techniques. For example, in information retrieval, the results of the query are grouped into small clusters, and each cluster has irrelevant results. By Clustering techniques, they are grouped into similar categories and each category is subdivided into sub-categories to assist in the exploration of queries output. There are various types of clustering methods, they are

- Hierarchical methods
- Partitioning methods
- Density-based
- Model-based clustering
- Grid-based model

The following are an overview of techniques used in data mining and artificial intelligence.

#### 1. Hierarchical Method

This method creates a cluster by partitioning in either a top-down and bottom-up manner. Both these approach produces dendrogram they make connectivity between them. The dendrogram is a tree-like format that keeps the sequence of merged clusters. Hierarchical methods are produced multiple partitions with respect to similarity levels. They are divided into Agglomerative hierarchical clustering and divisive hierarchical clustering. Here a cluster tree is created by using merging techniques. For the splitting process, divisive is used, merging uses agglomerative.

Agglomerative clustering involves :

- Initially taking all the data points and considering them as individual clusters start from a top-down manner. These clusters are merged until we obtained the desired results.
- The next two similar clusters are grouped together to form a huge single cluster.
- Again calculating proximity in the huge cluster and merge the similar clusters.
- The final step involves merging all the yielded clusters at each step to form a final single cluster.

#### 2. Partitioning Method

The main goal of partition is relocation. They relocate partitions by shifting from one cluster to another which makes an initial partitioning. It divides ‘n’ data objects into ‘k’ number of clusters. This partitional method is preferred more than a hierarchical model in pattern recognition.

The following criteria are set to satisfy the techniques:

- Each cluster should have one object.
- Each data object belongs to a single cluster.

The most commonly used Partition techniques are the K-mean Algorithm. They divide into ‘K’ clusters represented by centroids. Each cluster centre is calculated as a mean of that cluster and the R function visualizes the result.

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This algorithm has the following steps:

- Selecting K objects randomly from the data set and forms the initial centres (centroids)
- Next assigning Euclidean distance between the objects and mean centre.
- Assigning a mean value for each individual cluster.
- Centroid update steps for each ‘k’ Clusters.

#### 3. Density Model

In this model, clusters are defined by locating regions of higher density in a cluster. The main principle behind them is concentrating on two parameters: max radius of the neighbourhood and min number of points. The density-based model identifies clusters of different shapes and noise. It works by detecting patterns by estimating the spatial location and the distance to the neighbour’s method used here is DBSCAN (Density-based spatial clustering) which gives hands for large spatial databases. Using three data points for clustering namely Core points, Border points, and outliers. The primary goal is to identify the clusters and their distribution parameters. The clustering process is stopped with the need for density parameters. To find the clusters it is important to have a parameter Minimum features Per Cluster in calculating core-distance. The three different tools provided by this model are DBSCAN, HDBSCAN, Multi-scale.

#### 4. Model-Based Clustering

This model combines two or three clusters together from the data distribution. The basic idea behind this model is it is necessary to divide data into two groups based on the probability model (Multivariate normal distributions). Here each group is assigned as concepts or class. Each component is defined by a density function. To find the parameter in this model Maximum Likelihood estimation is used for the fitting of the mixture distribution. Each cluster ‘K’ is modelized by Gaussian distribution with a two-parameter µ_{k} mean vector and £_{k }covariance vector.

#### 5. Grid-Based Model

In this approach, the objects are considered to be space-driven by partitioning the space into a finite number of cells to form a grid. With the help of the grid, the clustering technique is applied for faster processing which is typically dependent on cells not on objects.

The steps involved are:

- Creation of grid structure
- Cell density is calculated for each cell
- Applying a sorting mechanism to their densities.
- Searching cluster centres and traversal on neighbour cells to repeat the process.

### Importance of Clustering Methods

- Having clustering methods helps in restarting the local search procedure and remove the inefficiency. Clustering helps to determine the internal structure of the data.
- This clustering analysis has been used for model analysis, vector region of attraction.
- Clustering helps in understanding the natural grouping in a dataset. Their purpose is to make sense to partition the data into some group of logical groupings.
- Clustering quality depends on the methods and to identify hidden patterns.
- They play a wide role in applications like marketing economic research, weblogs to identify patterns in similarity measures, Image processing, Spatial research.
- They are used in outlier detections to detect credit card fraudulence.

### Conclusion

Clustering is considered to be a general task to solve the problem which formulates optimization problems. It plays key importance in the field of data mining and data analysis. We have seen different clustering methods that divide the data set depends on the requirements. Most of the research is based on traditional techniques like K-means and hierarchical models. Cluster areas are applied in high dimensional states which form a future scope of researchers.

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