ML | Logistic Regression using Python

Difficulty Level : Medium
Last Updated : 29 Apr, 2019

Prerequisite: Understanding Logistic Regression

User Database – This dataset contains information of users from a companies database. It contains information about UserID, Gender, Age, EstimatedSalary, Purchased. We are using this dataset for predicting that a user will purchase the company’s newly launched product or not.

Data – User_Data

Let’s make the Logistic Regression model, predicting whether a user will purchase the product or not.

Inputing Libraries

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

Loading dataset – User_Data

dataset = pd.read_csv('...\\User_Data.csv')

Now, to predict whether a user will purchase the product or not, one needs to find out the relationship between Age and Estimated Salary. Here User ID and Gender are not important factors for finding out this.

# input
x = dataset.iloc[:, [2, 3]].values
  
# output
y = dataset.iloc[:, 4].values

Splitting the dataset to train and test. 75% of data is used for training the model and 25% of it is used to test the performance of our model.

from sklearn.cross_validation import train_test_split
xtrain, xtest, ytrain, ytest = train_test_split(
        x, y, test_size = 0.25, random_state = 0)

Now, it is very important to perform feature scaling here because Age and Estimated Salary values lie in different ranges. If we don’t scale the features then Estimated Salary feature will dominate Age feature when the model finds the nearest neighbor to a data point in data space.

from sklearn.preprocessing import StandardScaler
sc_x = StandardScaler()
xtrain = sc_x.fit_transform(xtrain) 
xtest = sc_x.transform(xtest)
  
print (xtrain[0:10, :])

Output :

[[ 0.58164944 -0.88670699]
 [-0.60673761  1.46173768]
 [-0.01254409 -0.5677824 ]
 [-0.60673761  1.89663484]
 [ 1.37390747 -1.40858358]
 [ 1.47293972  0.99784738]
 [ 0.08648817 -0.79972756]
 [-0.01254409 -0.24885782]
 [-0.21060859 -0.5677824 ]
 [-0.21060859 -0.19087153]]

Here once see that Age and Estimated salary features values are sacled and now there in the -1 to 1. Hence, each feature will contribute equally in decision making i.e. finalizing the hypothesis.

Finally, we are training our Logistic Regression model.

from sklearn.linear_model import LogisticRegression
classifier = LogisticRegression(random_state = 0)
classifier.fit(xtrain, ytrain)

After training the model, it time to use it to do prediction on testing data.

y_pred = classifier.predict(xtest)

Let’s test the performance of our model – Confusion Matrix

from sklearn.metrics import confusion_matrix
cm = confusion_matrix(ytest, y_pred)
  
print ("Confusion Matrix : \n", cm)

Output :

Confusion Matrix : 
 [[65  3]
 [ 8 24]]

Out of 100 :
TruePostive + TrueNegative = 65 + 24
FalsePositive + FalseNegative = 3 + 8

Performance measure – Accuracy

from sklearn.metrics import accuracy_score
print ("Accuracy : ", accuracy_score(ytest, y_pred))

Output :

Accuracy :  0.89

Visualizing the performance of our model.

from matplotlib.colors import ListedColormap
X_set, y_set = xtest, ytest
X1, X2 = np.meshgrid(np.arange(start = X_set[:, 0].min() - 1, 
                               stop = X_set[:, 0].max() + 1, step = 0.01),
                     np.arange(start = X_set[:, 1].min() - 1, 
                               stop = X_set[:, 1].max() + 1, step = 0.01))
  
plt.contourf(X1, X2, classifier.predict(
             np.array([X1.ravel(), X2.ravel()]).T).reshape(
             X1.shape), alpha = 0.75, cmap = ListedColormap(('red', 'green')))
  
plt.xlim(X1.min(), X1.max())
plt.ylim(X2.min(), X2.max())
  
for i, j in enumerate(np.unique(y_set)):
    plt.scatter(X_set[y_set == j, 0], X_set[y_set == j, 1],
                c = ListedColormap(('red', 'green'))(i), label = j)
      
plt.title('Classifier (Test set)')
plt.xlabel('Age')
plt.ylabel('Estimated Salary')
plt.legend()
plt.show()

Output :

Analysing the performance measures – accuracy and confusion matrix and the graph, we can clearly say that our model is performing really good.

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