This article was published as a part of the Data Science Blogathon.
Clustering is the process of grouping similar data together. It falls under the category of unsupervised learning, that is the input data does not have labeled responses. Clustering algorithms find their applications in various fields like finance, medicine, and e-commerce. One such example is in e-commerce a possible use case would be to group similar customer segments based on their purchasing styles to give them offers or discounts.
In clustering every data point belongs to some cluster however a single data point cannot be present in more than one cluster. The performance of a clustering algorithm can be measured by metrics such as the Dunn index (DI). A large inter-cluster distance(well separated) and a smaller inter-cluster distance(compact) clusters have a higher value of DI.
Different approaches can be employed in clustering based on your dataset, such as
We would focus on centroid-based clustering in this article.
K means algorithm is one of the centroid based clustering algorithms. Here k is the number of clusters and is a hyperparameter to the algorithm. The core idea behind the algorithm is to find k centroids followed by finding k sets of points which are grouped based on the proximity to the centroid such that the squared distances of the points in the cluster to the centroid are minimized. This optimization is a very hard problem hence an approximation is used to solve the problem. One such approximation is Lloyd’s algorithm whose implementation is as below.
The only problem with this implementation however is that it suffers from initialization sensitivity. On selecting different centroids in the initialization stage different clusters are generated. Workaround to the problem would be
In some cases it is difficult to interpret centroids, for example, if you are dealing with text data, centroids are not interpretable. An approach to deal with this would be to use the K medoids algorithm. It would select the most centered member within the data as a cluster center and is generally more robust to outliers than other means.
Elbow or knee method is used to determine the best k. We try the k means implementation for multiple k values and plot them against our sum of squared distances from the centroid(loss function). The elbow of the curve (where the curve visibly bends) is selected as the optimum k.
Let’s run through a code example of K means in action.
Try out the above code in the live coding window below:
from sklearn.datasets import make_blobs
from matplotlib import pyplot
from pandas import DataFrame
X,y = make_blobs(n_samples=100, n_features=2)
df = DataFrame(dict(x=X[:,0], y=X[:,1], label=y))
colors = {0:'red', 1:'blue', 2:'green'}
fig, ax = pyplot.subplots()
grouped = df.groupby('label')
for key, group in grouped:
group.plot(ax=ax, kind='scatter', x='x', y='y', label=key, color=colors[key])
#
print(df)
print("Columns \n\n")
print(df.columns)
df_X = df[['x','y']]
df_X
import sklearn.cluster
kmeans = sklearn.cluster.KMeans(n_clusters=3,init='k-means++',random_state=0).fit(df_X)
print("\n\n Cluster Center: \n\n ")
print(kmeans.cluster_centers_)
print("\n\n Lables")
print(kmeans.labels_)
We can see that our k means algorithm did a very good job in clustering our dataset.
For the entire code snippet:- https://www.kaggle.com/aliphya/k-means-clustering-example
Thank you for reading along, I am Alicia Ghantiwala a data science enthusiast and a software engineer at BNP Paribas.
My LinkedIn profile:- https://www.linkedin.com/in/alifia-ghantiwala-683403135/
The media shown in this article are not owned by Analytics Vidhya and is used at the Author’s discretion.
I investigate data on a daily basis to find insights! I write so that I can understand more clearly. Have completed my graduation in Computer Engineering, and won my first public data science competition last month, March 2021, hosted on Kaggle by Google Developers.
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