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How to find optimal number of n_neighbours in knn algorithm in python?


To find best fit n_neighbours in knn algorithm to improve performance of the model.


Iris data set


  Improved classification results.


  Import the library.

  Load the sample data set..

  Split the data train and test.

  Define the number of n_neighbours.

  Fit the train data into Gridsearch model.

  Find the optimal number of n_neighbours.

  Improve the model performance.

  Calculate precision, recall and accuracy.

Sample Code

#import libraries
import warnings
import numpy as np
import pandas as pd
from sklearn.model_selection import train_test_split
from sklearn.neighbors import KNeighborsClassifier
from sklearn.model_selection import GridSearchCV
from sklearn.metrics import classification_report, confusion_matrix, accuracy_score

#load the sample data from iris.csv file
data = pd.read_csv(‘/home/soft50/soft50/Sathish/practice/iris.csv’)

#Make it as a data frame
df = pd.DataFrame(data)

#feature variables
X = df.iloc[:,0:4]
y = df.iloc[:,4]

#Split the data into train and testing
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.3, random_state=0)

knn = KNeighborsClassifier()
#create a dictionary of all values we want to test for n_neighbors
params_knn = {‘n_neighbors’: np.arange(1, 25)}
#use gridsearch to test all values for n_neighbors
knn_gs = GridSearchCV(knn, params_knn, cv=5)
#fit model to training data, y_train)
knn_best = knn_gs.best_estimator_
print(“Optimal number of n_neighbours\n\n”,knn_best)
y_pred = knn_best.predict(X_test)

#Evaluate the model
print(“Classification report for KNN\n”)
print(classification_report(y_test, y_pred))
print(“Confusion matrix\n”)
print(confusion_matrix(y_test, y_pred))
print(“Accuracy score”)
print(accuracy_score(y_test, y_pred))

find optimal number of n_neighbours in knn algorithm in python