There are two ways to plot a confusion matrix in Python using the Scikit-Learn library: plot_confusion_matrix (deprecated) and ConfusionMatrixDisplay.
Plot a Confusion Matrix with ConfusionMatrixDisplay
The alternative is to use ConfusionMatrixDisplay.
import matplotlib.pyplot as plt
from sklearn.metrics import ConfusionMatrixDisplay
from sklearn.metrics import confusion_matrix
cm = confusion_matrix(y_test, y_pred, labels=knn.classes_)
color = 'white'
disp = ConfusionMatrixDisplay(confusion_matrix=cm, display_labels=knn.classes_)
disp.plot()
plt.show()
Plot the Confusion Matrix with plot_confusion_matrix (deprecated)
You can use the plot_confusion_matrix method to visualize the confusion matrix.
import matplotlib.pyplot as plt
from sklearn.metrics import plot_confusion_matrix
color = 'white'
matrix = plot_confusion_matrix(knn, X_test, y_test, cmap=plt.cm.Blues)
matrix.ax_.set_title('Confusion Matrix', color=color)
plt.xlabel('Predicted Label', color=color)
plt.ylabel('True Label', color=color)
plt.gcf().axes[0].tick_params(colors=color)
plt.gcf().axes[1].tick_params(colors=color)
plt.show()
The result is your confusion matrix plot.
- Top left quadrant = True Positives = Number of benign labelled as benign
- Bottom right quadrant = True Negatives = Number of malignant labelled as malignant
- Top right quadrant = False Positives = Number of benign labelled as malignant
- Bottom left quadrant = False Negatives = Number of malignant labelled as benign
You may run into this error:
ImportError: cannot import name 'plot_confusion_matrix' from 'sklearn.metrics'
Or the following FutureWarning:
FutureWarning: Function plot_confusion_matrix is deprecated; Function `plot_confusion_matrix` is deprecated in 1.0 and will be removed in 1.2. Use one of the class methods: ConfusionMatrixDisplay.from_predictions or ConfusionMatrixDisplay.from_estimator.
warnings.warn(msg, category=FutureWarning)
This is because plot_confusion_matrix was deprecated in some release.
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