diff --git a/machine_learning/logistic_regression.py b/machine_learning/logistic_regression.py new file mode 100644 index 000000000000..70c0b2807b7f --- /dev/null +++ b/machine_learning/logistic_regression.py @@ -0,0 +1,97 @@ +#!/usr/bin/env python +# coding: utf-8 + +# # Logistic Regression from scratch + +# In[62]: + + +''' Implementing logistic regression for classification problem + Helpful resources : 1.Coursera ML course 2.https://medium.com/@martinpella/logistic-regression-from-scratch-in-python-124c5636b8ac''' + + +# In[63]: + + +#importing all the required libraries +import numpy as np +import matplotlib.pyplot as plt +get_ipython().run_line_magic('matplotlib', 'inline') +from sklearn import datasets + + +# In[67]: + + +#sigmoid function or logistic function is used as a hypothesis function in classification problems +def sigmoid_function(z): + return 1/(1+np.exp(-z)) + + +def cost_function(h,y): + return (-y*np.log(h)-(1-y)*np.log(1-h)).mean() + +# here alpha is the learning rate, X is the featue matrix,y is the target matrix +def logistic_reg(alpha,X,y,max_iterations=70000): + converged=False + iterations=0 + theta=np.zeros(X.shape[1]) + + num_iterations=0 + while not converged: + z=np.dot(X,theta) + h=sigmoid_function(z) + gradient = np.dot(X.T,(h-y))/y.size + theta=theta-(alpha)*gradient + + z=np.dot(X,theta) + h=sigmoid_function(z) + e=cost_function(h,y) + print('J=',e) + J=e + + iterations+=1 #update iterations + + + if iterations== max_iterations: + print("Maximum iterations exceeded!") + converged=True + + return theta + + + + + + + + +# In[68]: + + +if __name__=='__main__': + iris=datasets.load_iris() + X = iris.data[:, :2] + y = (iris.target != 0) * 1 + + alpha=0.1 + theta=logistic_reg(alpha,X,y,max_iterations=70000) + print(theta) + def predict_prob(X): + return sigmoid_function(np.dot(X,theta)) # predicting the value of probability from the logistic regression algorithm + + + plt.figure(figsize=(10, 6)) + plt.scatter(X[y == 0][:, 0], X[y == 0][:, 1], color='b', label='0') + plt.scatter(X[y == 1][:, 0], X[y == 1][:, 1], color='r', label='1') + x1_min, x1_max = X[:,0].min(), X[:,0].max(), + x2_min, x2_max = X[:,1].min(), X[:,1].max(), + xx1, xx2 = np.meshgrid(np.linspace(x1_min, x1_max), np.linspace(x2_min, x2_max)) + grid = np.c_[xx1.ravel(), xx2.ravel()] + probs = predict_prob(grid).reshape(xx1.shape) + plt.contour(xx1, xx2, probs, [0.5], linewidths=1, colors='black'); + + plt.legend(); + + +