What is K-means Clustering in Machine Learning?

  • Neelam Tyagi
  • Mar 14, 2020
  • Machine Learning
What is K-means Clustering in Machine Learning? title banner

Clustering is the immense pool of technologies to catch classes of observations (known as clusters) under a dataset provided, that contribute identical features. 


Clustering is arranged in a way that each observation in the same class possesses similar characteristics and observation of separate groups shows dissimilarity in characteristics. 


As a part of the unsupervised learning method, clustering attempts to identify a relationship between n-observations( data points) without being trained by the response variable.


With the intent of obtaining data points under the same class as identical as possible, and the data points in a separate class as dissimilar as possible.


Basically, in the process of clustering, one can identify which observations are alike and classify them significantly in that manner. However, clustering is different from classification, learn here how!! 


Keeping this perspective in mind, k-means clustering is the most straightforward and frequently practiced clustering method to categorize a dataset into a bunch of k classes (groups).


This blog serves as an introduction to the k-means clustering method with an example, its difference with hierarchical clustering and at last limitations of k-means clustering.  





Beginning with Unsupervised Learning, a part of machine learning where no response variable is present to provide guidelines in the learning process and data is analyzed by algorithms itself to identify the trends. 


Opposite to that, supervised learning is where existing data is already labeled and you know which behavior you want to recognize from new datasets, unsupervised learning doesn’t exhibit labeled dataset and algorithms are there to explore relationships and patterns in the data.


It is a known fact that the data and information are usually obscured by noise and redundancy so making it into groups with similar features is the decisive action to bring some insights.


“You can have data without information, but you cannot have information without data.”  - Daniel Keys Moran


One of the excellent methods in unsupervised machine learning treated for data classification, k-means suits well for exploratory data analysis. To understand data perfectly and get inferences from all data types despite the data in the form of images ( Prefered blog: Generative Adversarial Network (GAN) in Unsupervised Machine Learning), text content or numeric, k-means works flexibly. 



What is k-means clustering?


K-means algorithm explores for a preplanned number of clusters in an unlabelled multidimensional dataset, it concludes this via an easy interpretation of how an optimized cluster can be expressed. 


Primarily the concept would be in two steps, firstly,  the cluster center is the arithmetic mean (AM) of all the data points associated with the cluster. Secondly, each point is adjoint to its cluster center in comparison to other cluster centers. These two interpretations are the foundation of the k-means clustering model.


You can take the center as a data point that outlines the means of the cluster, also it might not possibly be a member of the dataset. 


You can learn k-means clustering by the example given in the following video,


Convenience with K-means


Find below some key features of k-means clustering;


  1. It is very smooth in terms of interpretation and resolution.

  2. For a large number of variables present in the dataset, K-means operates quicker than Hierarchical clustering. 

  3. While redetermining the cluster center, an instance can modify the cluster. 

  4. K-means reforms compact clusters.

  5. It can work on unlabeled numerical data.


Limitations with K-means


The following are few limitations with K-Means clustering;


  1. Sometimes, it is quite tough to forecast the number of clusters, or the value of k.

  2. The output is highly influenced by original input, for example, the number of clusters.

  3. An array of data substantially hits the concluding outcomes.

  4. In some cases, clusters show complex spatial views, then executing clustering is not a good choice.

  5. Also, rescaling is sometimes conscious, it can’t be done by normalization or standardization of data points, the output gets changed entirely.



Expectation-Maximization: K-means Algorithm


K-Means is just the Expectation-Maximization (EM) algorithm, It is a persuasive algorithm that exhibits a variety of context in data science, the E-M approach incorporates two parts in its procedure;


1. To assume some cluster centers,

2. Rerun as far as transformed;

  •  E-Step: To appoint data points to the closest cluster center,

  •   M-Step: To introduce the cluster centers to the mean.


Where the E-step is the Expectation step, it comprises upgrading forecasts of associating the data point with the respective cluster. 


And, M-step is the Maximization step, it includes maximizing some features that specify the region of the cluster centers, for this maximization is expressed by considering the mean of the data points of each cluster. 


In account with some critical possibilities, each reiteration of E-step and M-step algorithm will always yield in terms of improved estimation of clusters’ characteristics. 


K-means utilize an iterative procedure to yield its final clustering based on the number of predefined clusters, as per need according to the dataset and represented by the variable K. 


For instance, if K is set to 3 (k3), then the dataset would be categorized in 3 clusters if k is equal to 4, then the number of clusters will be 4 and so on. 


The fundamental aim is to define k centers, one for each cluster, these centers must be located in a sharp manner because of the various allocation causes different outcomes. So, it would be best to put them as far away as possible from each other.


Also, The maximum number of plausible clusters will be the same as the total number of observations/features present in the dataset.



How the k-means algorithm works


Don’t you get excited !!! Yes, you must be, let’s move ahead with the notion of working algorithm.


By specifying the value of k, you are informing the algorithm of how many means or centers you are looking for. Again repeating, if k is equal to 3, the algorithm accounts it for 3 clusters. 


Following are the steps for working of the k-means algorithm;


  • K-centers are modeled randomly in accordance with the present value of K.


  • K-means assigns each data point in the dataset to the adjacent center and attempts to curtail Euclidean distance between data points. Data points are assumed to be present in the peculiar cluster as if it is nearby to center to that cluster than any other cluster center. 


  • After that, k-means determines the center by accounting the mean of all data points referred to that cluster center. It reduces the complete variance of the intra-clusters with respect to the prior step.  Here, the “means” defines the average of data points and identifies a new center in the method of k-means clustering.

The image interprets the clustering of some objects on the basis of their shapes, they can also be classified on the basis of color.

Clustering of data points (objects in this case)

  • The algorithm gets repeated among the steps 2 and 3 till some paradigm will be achieved such as the sum of distances in between data points and their respective centers are diminished, an appropriate number of iterations is attained, no variation in the value of cluster center or no change in the cluster due to data points. 



Application of K-means Clustering


The concern of the fact is that the data is always complicated, mismanaged, and noisy. The conditions in the real world cast hardly the clear picture to which these types of algorithms can be applied. Let’s learn where we can implement k-means clustering.


  1. K-means clustering is applied in the Call Detail Record (CDR) Analysis. It gives in-depth vision about customer requirements and satisfaction on the basis of call-traffic during the time of the day and demographic of a particular location.


  1. It is used in the clustering of documents to identify the compatible documents in the same place. ( See another dimensionality reduction technique for documents analysis: Principal Component Analysis)


  1. It is deployed to classify the sounds on the basis of their identical patterns and segregate malformation in them.   


  1. It serves as the model of lossy images compression technique, in the confinement of images, K-means makes clusters pixels of an image in order to decrease the total size of it. (You must read, What is Deepfake Technology and how it may be harmful, to learn more image analysis in ML)


  1. It is helpful in the business sector for recognizing the portions of purchases made by customers, also to cluster movements on apps and websites.


  1. In the field of insurance and fraud detection on the basis of prior data, it is plausible to cluster fraudulent consumers to demand based on their proximity to clusters as the patterns indicate. (Reference Blog: Banking on Artificial Intelligence (AI)



Distinguishing between K-means Clustering and Hierarchical Clustering 


  1. K-means clustering produces a specific number of clusters for the disarranged and flat dataset, where Hierarchical clustering builds a hierarchy of clusters, not for just a partition of objects.


  1. K-means can be used for categorical data and first converted into numeric by assigning rank, where Hierarchical clustering was selected for categorical data but due to its complexity, a new technique is considered to assign rank value to categorical features.


  1. K-means are highly sensitive to noise in the dataset and perform well than Hierarchical clustering where it is less sensitive to noise in a dataset.


  1. Performance of the K-Means algorithm increases as the RMSE decreases and the RMSE decreases as the number of clusters increases so the time of execution increases, in contrast to this, the performance of Hierarchical clustering is less. 


  1. K-means are good for a large dataset and Hierarchical clustering is good for small datasets.





K-means clustering is the unsupervised machine learning algorithm that is part of a much deep pool of data techniques and operations in the realm of Data Science. It is the fastest and most efficient algorithm to categorize data points into groups even when very little information is available about data. 


More on, similar to other unsupervised learning, it is necessary to understand the data before adopting which technique fits well on a given dataset to solve problems. Considering the correct algorithm, in return, can save time and efforts and assist in obtaining more accurate results. 


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