Different Types of Clustering Algorithm in Unsupervised  Learning 

K-means clustering: 

K-means clustering is the most used clustering algorithm. A centroid-based algorithm  and a very simple unattended learning algorithm. This algorithm attempts to reduce the  variation in data points within a collection. It is a way for many people to be informed  about unsupervised machine learning. K means methods are best used in small data sets  because they run over all data points. That means it will take a lot of time to separate data  points if there is a large number of them in the data set. 

Implementation: 

Let’s import the toy dataset from scikit-learn and visualize the data points of dataset  make_blobs using 4 clusters with 1000 samples, 

import matplotlib.pyplot as plt  from sklearn.datasets import make_blobs  # create dataset  X, y = make_blobs(n_samples=1000, n_features=2,   centers=4, cluster_std=0.5,   shuffle=True, random_state=0)  # plot  plt.scatter(X[:, 0], X[:, 1],   c=’blue’, marker=’o’,   edgecolor=’red’, s=100)  plt.show()

Output:

The dataset that we just created consists of 1000 randomly generated points that are  grouped into four groups. 

 

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Apply KMeans Model: 

set the number of desired clusters to 4 , init to random , n_init to 15 and max_iter =300 

from sklearn.cluster import KMeans  kmeans_model = KMeans(n_clusters=4, init=’random’,  n_init=15, max_iter=300,random_state=0)  y_pred = kmeans_model.fit_predict(X)

 

Plotting Results: 

Use scatter plot for plotting result for predicted output, 

for i in range(4):   plt.scatter(   X[y_pred == i, 0], X[y_pred == i, 1],   s=50, c=’lightgreen’,   marker=’o’, edgecolor=’black’)  # plot the centroids of each clusters  plt.scatter(   kmeans_model.cluster_centers_[:, 0],   kmeans_model.cluster_centers_[:, 1],   s=100, marker=’s’,   c=’red’, edgecolor=’black’,   label=’centroids of clusters’  )  plt.legend(scatterpoints=1)  plt.show()

 

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Output:

 

Choice of Right Number of clusters: 

Elbow method is useful for this we can choose write number of clusters as follows, 

inertia = []  for i in range(1, 11):   kmeans_model = KMeans(n_clusters=i, init=’random’,  n_init=15, max_iter=300,random_state=0)   kmeans_model.fit(X)   inertia.append(kmeans_model.inertia_)  # plot  plt.plot(range(1, 11), inertia, color=’red’,marker=’s’) plt.plot(range(1, 11), inertia,color=’green’)  plt.xlabel(‘clusters Number’)  plt.ylabel(‘Inertia of Each clusters’)  plt.show()

 

Output: 

 

From the above graph we can conclude that only four clusters are possible as graph after  cluster number 4 remains steady.

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DBSCAN clustering: 

DBSCAN stands for density-based spatial clustering of applications with noise. It is an  algorithm at the level of human resilience, in contrast to the k methods. This is a great  algorithm for finding outsiders in a set of data. It receives randomly generated clusters  depending on the number of data points in the various regions. It divides the regions into  low-lying areas so that it can find the outside among the larger groups. This algorithm is  better than k-means when it comes to working with randomly generated data. DBSCAN  uses two parameters to determine how clusters are defined: minPts (the minimum  number of data points that need to be grouped together in an area to be considered the  maximum) and eps (the distance used to determine whether a data point is in the same  area as other data points). Selecting the appropriate first parameters is essential for this  algorithm to work. 

Implementation: 

Dataset is same as like above, 

Apply KMeans Model: 

set the eps and min_samples to 0.3 and 30 respectively, 

from sklearn.cluster import DBSCAN  db_scan = DBSCAN(eps=0.3, min_samples=30)  db_scan.fit(X)  y_pred = db_scan.fit_predict(X)

 

Plotting Results: 

Use scatter plot for plotting result for predicted output, 

plt.figure(figsize=(10,6))  plt.scatter(X[:,0], X[:,1],c=y_pred,s=100,marker=’o’,  edgecolor=’black’)  plt.title(“Clusters determined by DBSCAN clustering”)

 

Output:

 

When clusters have no spherical shape then the above algorithm will not work properly  for we can use Gaussian mixture model clustering. 

 

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Gaussian mixture model clustering: 

If data follows a circular pattern then only k-means is going to work. The k-method means  that calculating the distance between data points is related to the circular path, so non circular data is not well integrated. This is a problem that is being addressed by the  Gaussian hybrids. You do not need circular data to work properly. 

The Gaussian mixture model uses multiple Gaussian distributions to match the data set  to its liking. There are many single Gaussian models that act as hidden layers in this  hybrid model. The model therefore calculates the probability that the data point belongs  to a particular distribution of Gaussian and that is the group that will fall into it. 

Implementation: 

Let’s import the toy dataset from scikit-learn and visualize the data points Use scatter plot for plotting result for predicted output, 

import matplotlib.pyplot as plt  from sklearn.datasets import make_blobs  X, y = make_blobs(n_samples=1000, n_features=2,   centers=2, cluster_std=0.5,   shuffle=True, random_state=0)  import numpy as np  rng = np.random.RandomState(13)  X_stretched = np.dot(X, rng.randn(2, 2))  plt.scatter(X_stretched[:, 0], X_stretched[:, 1],  c=’blue’, marker=’o’,   edgecolor=’red’, s=100)  plt.show()

 

Output:

 

The dataset that we just created consists of 1000 randomly generated points that are  grouped into two groups. 

 

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Apply Gaussian Mixture Model: 

set the number of desired clusters to 2 i.e. n_components, 

from sklearn.mixture import GaussianMixture  gmm = GaussianMixture(n_components=2)  gmm.fit(X_stretched)  y_pred = gmm.fit_predict(X_stretched)

 

Plotting Results: 

Use scatter plot for plotting result for predicted output, 

plt.figure(figsize=(10,6))  plt.scatter(X_stretched[:,0],   X_stretched[:,1],c=”red”,s=100,marker=’o’, edgecolor=’black’)

 

Output:

 

BIRCH clustering: 

The Balance Iterative Reducing and Clustering using Hierarchies (BIRCH) algorithm  works well on huge data sets but the k-means algorithm will work on small datasets. Breaks data into small summaries included instead of initial data points. Summaries  contain as much distribution information about data points as possible. This algorithm  is commonly used with other algorithm collections because other integration techniques  can be used in summaries created by BIRCH. 

The worst thing about the BIRCH algorithm is that it only works on numerical data values.  You cannot use this with category values unless you have made some data changes. 

Implementation: 

Let’s import the toy dataset from scikit-learn and visualize the data points 

from sklearn.cluster import Birch  import matplotlib.pyplot as plt  X, clusters = make_blobs(n_samples=600, centers=4,  cluster_std=0.80, random_state=32)  plt.scatter(X[:, 0], X[:, 1],   c=’blue’, marker=’o’,   edgecolor=’red’, s=100)  plt.show()

 

Output: 

The dataset that we just created consists of 600 randomly generated points that are  grouped into four groups.

Apply BIRCH clustering: 

Branching factor and threshold value is only assigned 

brc_model = Birch(branching_factor=100, n_clusters=None,  threshold=1.5)  brc_model.fit(X)  y_pred = brc_model.predict(X)

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Plotting Results: 

Use scatter plot for plotting result for predicted output, 

plt.figure(figsize=(10,6))  plt.scatter(X[:,0], X[:,1], c=y_pred,   cmap=’rainbow’,edgecolor=’black’,s=100)

 

Output: 

OPTICS clustering: 

OPTICS stands for Ordering Points to Identify the Clustering Structure. A density-based  algorithm similar to DBSCAN, but better because it can find logical collections of data  that vary widely. It does this by ordering data points so that the points closest to the  neighbors are in order. This makes it easier to find different clusters. The OPTICS 

algorithm processes each data point once, similar to DBSCAN (albeit slower than  DBSCAN). There is also a special distance reserved for each data point that indicates a  point belonging to a particular group. 

Implementation: 

Dataset is same as above, 

Apply OPTICS clustering: 

Here we have assigned desired values to min_samples,xi and min_cluster_size as  follows, 

from sklearn.cluster import OPTICS  op_model = OPTICS(min_samples=40, xi=0.02,   min_cluster_size=0.1)  y_op_pred=op_model.fit_predict(X)

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Plotting Results: 

Use scatter plot for plotting result for predicted output, 

plt.figure(figsize=(10,6))  plt.scatter(X[:,0], X[:,1], c=y_op_pred,   cmap=’rainbow’,edgecolor=’black’,s=100)

 

 

Author:
Amol Kamble

 

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