K-Nearest Neighbor (KNN) algorithm is a popular machine learning technique used for classification and regression analysis. It is a non-parametric algorithm that uses a simple method to find the nearest neighbors of a given data point. KNN algorithm can be applied to various domains, including image recognition, natural language processing, and recommendation systems.

In this guide, we will provide a comprehensive overview of the KNN algorithm, its advantages, and how to implement it in Python.

## What is K-Nearest Neighbor Algorithm?

The K-Nearest Neighbor (KNN) algorithm is a non-parametric algorithm used for classification and regression analysis. It is a type of instance-based learning where the algorithm uses the training data to make predictions for the new data points.

The KNN algorithm is based on the assumption that similar data points tend to belong to the same class. It works by finding the K nearest neighbors of the new data point and assigning it to the most common class among those neighbors.

### How Does KNN Algorithm Work?

The KNN algorithm works in the following steps:

• Calculate the distance between the new data point and all the training data points.
• Select the K nearest neighbors based on the calculated distance.
• Assign the new data point to the class that has the highest number of neighbors.

The distance between two data points can be calculated using various distance metrics, including Euclidean distance, Manhattan distance, and Minkowski distance.

The KNN algorithm has several advantages, including:

• Simple and easy to implement.
• Non-parametric, which means it does not make any assumptions about the underlying data distribution.
• Can be used for both classification and regression analysis.
• Robust to noisy data.

## How to Implement KNN Algorithm in Python?

Now, let’s see how to implement the KNN algorithm in Python. We will use the scikit-learn library, which provides a simple and easy-to-use implementation of the KNN algorithm.

First, we need to import the necessary libraries:

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from sklearn.neighbors import KNeighborsClassifier

from sklearn.model_selection import train_test_split

Next, we load the iris dataset:

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X = iris.data

y = iris.target

We split the dataset into training and testing sets:

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X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.3)

Finally, we create an instance of the KNeighborsClassifier and fit it to the training data:

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knn = KNeighborsClassifier(n_neighbors=3)

knn.fit(X_train, y_train)

To make predictions for new data points, we use the predict method:

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y_pred = knn.predict(X_test)

And we can evaluate the performance of the model using various metrics, including accuracy, precision, recall, and F1-score.

## Conclusion

The K-Nearest Neighbor (KNN) algorithm is a popular machine learning technique used for classification and regression analysis. It is simple, easy to implement, and can be used for various domains. In this guide, we provided a comprehensive overview of the KNN algorithm, its advantages, and how to implement it in Python using the scikit-learn library.

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