Use python to draw confusion matrix (confusion_matrix)

Summary

When it comes to classification problems, we often need to analyze the experimental results by visualizing the confusion matrix to get the idea of ​​parameter adjustment. This article introduces how to use python to draw the confusion matrix (confusion_matrix). This article only provides the code and gives the necessary comments.

Code

# -*-coding:utf-8-*-
from sklearn.metrics import confusion_matrix
import matplotlib.pyplot as plt
import numpy as np

#labels表示你不同类别的代号，比如这里的demo中有13个类别
labels = ['A', 'B', 'C', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O']

#y_true代表真实的label值 y_pred代表预测得到的lavel值
y_true = np.loadtxt('../Data/re_label.txt')
y_pred = np.loadtxt('../Data/pr_label.txt')

tick_marks = np.array(range(len(labels))) + 0.5


def plot_confusion_matrix(cm, title='Confusion Matrix', cmap=plt.cm.binary):
    plt.imshow(cm, interpolation='nearest', cmap=cmap)
    plt.title(title)
    plt.colorbar()
    xlocations = np.array(range(len(labels)))
    plt.xticks(xlocations, labels, rotation=90)
    plt.yticks(xlocations, labels)
    plt.ylabel('True label')
    plt.xlabel('Predicted label')


cm = confusion_matrix(y_true, y_pred)
np.set_printoptions(precision=2)
cm_normalized = cm.astype('float') / cm.sum(axis=1)[:, np.newaxis]
print cm_normalized
plt.figure(figsize=(12, 8), dpi=120)

ind_array = np.arange(len(labels))
x, y = np.meshgrid(ind_array, ind_array)

for x_val, y_val in zip(x.flatten(), y.flatten()):
    c = cm_normalized[y_val][x_val]
    if c > 0.01:
        plt.text(x_val, y_val, "%0.2f" % (c,), color='red', fontsize=7, va='center', ha='center')
# offset the tick
plt.gca().set_xticks(tick_marks, minor=True)
plt.gca().set_yticks(tick_marks, minor=True)
plt.gca().xaxis.set_ticks_position('none')
plt.gca().yaxis.set_ticks_position('none')
plt.grid(True, which='minor', linestyle='-')
plt.gcf().subplots_adjust(bottom=0.15)

plot_confusion_matrix(cm_normalized, title='Normalized confusion matrix')
# show confusion matrix
plt.savefig('../Data/confusion_matrix.png', format='png')
plt.show()

Result

Instructions

Replace labels, y_true and y_pred with your own data according to the comments in the code.

Reference

How to draw confusion matrix with python