Cosmic Techie

Perceptron

Perceptron is a supervised learning algorithm for classification. It was originally proposed by Frank Rosenblatt and, refined and carefully analyzed by Marvin Minsky and Seymour Papert in 1969. The model is known as Perceptron Model.

Import Libraries

import numpy as np
import matplotlib.pyplot as plt
import pandas as pd
from sklearn.metrics import accuracy_score
%matplotlib inline

Perceptron Class

class Perceptron:

    def __init__(self, learning_rate=0.01, n_iters=1000):
        self.lr = learning_rate
        self.n_iters = n_iters
        self.activation_func = self._unit_step_func
        self.weights = None
        self.bias = None

    def fit(self, X, y):
        n_samples, n_features = X.shape
        self.weights = np.zeros(n_features) #Initializing weights 
        self.bias = 0

        y_ = np.array([1 if i > 0 else 0 for i in y])

        for _ in range(self.n_iters):
            
            for idx, x_i in enumerate(X):

                net_input = np.dot(x_i, self.weights) + self.bias
                y_predicted = self.activation_func(net_input)
                
                # Perceptron update rule
                update = self.lr * (y_[idx] - y_predicted)

                self.weights += update * x_i
                self.bias += update

    def predict(self, X):
        net_input = np.dot(X, self.weights) + self.bias
        y_predicted = self.activation_func(net_input)
        return y_predicted

    def _unit_step_func(self, x):
        return np.where(x>=0, 1, 0)

Read Data

df = pd.read_csv('https://archive.ics.uci.edu/ml/machine-learning-databases/iris/iris.data', header=None)
df.columns=['Sepal_length','Sepal_width','Petal_length','Petal_width','Species']
print(df[0:100])

y = df.iloc[0:100, 4].values
y = np.where(y == 'Iris-setosa', 0, 1)

# sepal length and petal length
X = df.iloc[0:100, [0,1,2,3]].values

Plotting

plt.scatter(X[:50, 0], X[:50, 1],
            color='green', marker='x', label='setosa')
plt.scatter(X[50:100, 0], X[50:100, 1],
            color='red', marker='o', label='versicolor')
plt.xlabel('sepal length')
plt.ylabel('petal length')
plt.legend(loc='upper right')
plt.show()

Applying Perceptron

from sklearn.model_selection import train_test_split

X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=5)
p = Perceptron(learning_rate=0.01, n_iters=1000)
p.fit(X_train, y_train)
predictions = p.predict(X_test)
print("True Values from the testing data:",y_test)
print("Predictions on the testing data:",predictions)
print("Perceptron classification accuracy", accuracy_score(y_test, predictions))

Notebook: