Python Program to Create K Nearest Neighbour Classifier Assignment Solution

Instructions

Objective

Write a program to create K nearest neighbour classifier in python.

Requirements and Specifications

Source Code

# -*- coding: utf-8 -*- import pandas as pd import numpy as np from sklearn.model_selection import train_test_split import matplotlib.pyplot as plt data_url = "http://lib.stat.cmu.edu/datasets/boston" raw_df = pd.read_csv(data_url, sep="\s+", skiprows=22, header=None) raw_df.head() data = np.hstack([raw_df.values[::2, :], raw_df.values[1::2, :2]]) target = raw_df.values[1::2, 2] """## Split into Train and Test""" X_train, X_test, y_train, y_test = train_test_split(data, target, test_size = 0.33, random_state = 42) X_train = np.array([ [5, 45], [5.11, 26], [5.6, 30], [5.9, 34], [4.8, 40], [5.8, 36], [5.3, 19], [5.8, 28], [5.5, 23], [5.6, 32], ]) y_train = np.array([77, 47, 55, 59, 72, 60, 40, 60, 45, 58]) X_test = np.array([ [5.5, 38] ]) y_test = np.array([65.2]) """## Define function to calculate the euclidean distance""" def euclidean_distance(X, x): return np.sqrt(np.sum(np.power(X-x,2), axis=1)) """## Define K """ K = 3 """## Function to predict""" def predict(x, X_train, y_train, K): # Compute euclidean distances D = euclidean_distance(X_train, x) # Sort in ascending order D = np.argsort(D) # Pick index of last K elements D_ = D[:K] # Get target values of the select K elements y_ = y_train[D_] # Calculate mean yi = np.mean(y_) return yi """## Estimate""" y_pred = np.zeros(y_test.shape) for i, x in enumerate(X_test): yi = predict(x, X_train, y_train, K) # Store predicted value y_pred[i] = yi """## Compute error""" err = np.sqrt(1/len(y_test) *np.sum(np.power(y_test-y_pred, 2))) print("The RMSE error is: {:.4f}".format(err)) """## Compute error for different values of K""" errors = list() for k in range(1, 10): y_pred = np.zeros(y_test.shape) for i, x in enumerate(X_test): yi = predict(x, X_train, y_train, k) y_pred[i] = yi # Compute error err = np.sqrt(1/len(y_test) *np.sum(np.power(y_test-y_pred, 2))) errors.append(err) # Plot plt.figure() plt.plot(range(1, 10), errors) plt.grid(True) plt.show() """### We see that the optimal value of K is K = 5"""