• • K-Nearest Neighbour is one of the simplest Machine Learning algorithms based on Supervised Learning technique.
• • K-NN algorithm assumes the similarity between the new case/data and available cases and put the new case into the category that is most similar to the available categories.
• • K-NN algorithm stores all the available data and classifies a new data point based on the similarity. This means when new data appears then it can be easily classified into a well suite category by using K- NN algorithm.
• • K-NN algorithm can be used for Regression as well as for Classification but mostly it is used for the Classification problems.
• • K-NN is a non-parametric algorithm, which means it does not make any assumption on underlying data.
• • It is also called a lazy learner algorithm because it does not learn from the training set immediately instead it stores the dataset and at the time of classification, it performs an action on the dataset.
• • KNN algorithm at the training phase just stores the dataset and when it gets new data, then it classifies that data into a category that is much similar to the new data.

Suppose there are two categories, i.e., Category A and Category B, and we have a new data point x1, so this data point will lie in which of these categories. To solve this type of problem, we need a K-NN algorithm. With the help of K-NN, we can easily identify the category or class of a particular dataset. Consider the below diagram:

How does K-NN work?

The K-NN working can be explained on the basis of the below algorithm:

• • Step-1: Select the number K of the neighbors
• • Step-2: Calculate the Euclidean distance of K number of neighbors
• • Step-3: Take the K nearest neighbors as per the calculated Euclidean distance.
• • Step-4: Among these k neighbors, count the number of the data points in each category.
• • Step-5: Assign the new data points to that category for which the number of the neighbor is maximum.
• • Step-6: Our model is ready.

Advantages of KNN Algorithm:

• • It is simple to implement.
• • It is robust to the noisy training data
• • It can be more effective if the training data is large.

Disadvantages of KNN Algorithm:

• • Always needs to determine the value of K which may be complex some time.
• • The computation cost is high because of calculating the distance between the data points for all the training samples.