Why does this confusion matrix (matplotlib) look squished in Jupyter Notebook?

Question

I'm running the code below for a confusion matrix. The output looked great until I reset the notebook kernal. I didn't change the code, but now it looks squished (Fig 1). It corrects when I delete the plt.yticks line (Fig 2), but I want those labels. This is probably simple, but I'm new to Python.

import itertools
def plot_confusion_matrix(cm, classes,
                          normalize=False,
                          title='Confusion Matrix',
                          cmap=plt.cm.Blues):
    """
    This function prints and plots the confusion matrix.
    Normalization can be applied by setting `normalize=True`.
    Source: http://scikit-learn.org/stable/auto_examples/model_selection/plot_confusion_matrix.html
    """
    if normalize:
        cm = cm.astype('float') / cm.sum(axis=1)[:, np.newaxis]
        print("Normalized confusion matrix")
    else:
        print('Confusion matrix, without normalization')

    print(cm)

    # Plot the confusion matrix
    plt.figure(figsize = (6, 6))
    plt.imshow(cm, interpolation='nearest', cmap=cmap)
    plt.title(title, size = 25)
    plt.colorbar(aspect=5)
    tick_marks = np.arange(len(classes))
    plt.xticks(tick_marks, classes, rotation=45, size = 12)
    plt.yticks(tick_marks, classes, size = 12)

    fmt = '.2f' if normalize else 'd'
    thresh = cm.max() / 2.

    # Labeling the plot
    for i, j in itertools.product(range(cm.shape[0]), range(cm.shape[1])):
        plt.text(j, i, format(cm[i, j], fmt), fontsize = 20,
                 horizontalalignment="center",
                 color="white" if cm[i, j] > thresh else "black")

    plt.grid(False)
    plt.tight_layout()
    plt.ylabel('Actual label', size = 15)
    plt.xlabel('Predicted label', size = 15)

cm = confusion_matrix(y_test, y_pred)
plot_confusion_matrix(cm, classes = ['Good Mental Health', 'Poor Mental Health'],
                      title = 'Confusion Matrix')

Answer 1

Try adding these lines at the end of the code.

plt.tight_layout()
plt.show()

This alone should help a lot. Some more advice:

1) I think what is happening is that you ask for a 6x6 inches figures, and this space includes the labels. A larger figure may help.

2) you could try to improve the way the space you require is used. I would for sure ask for the label to be in two different lines: I guess you have

 tick_marks = ['good mental health', 'poor mental health']

somewhere in your code. Doing

 tick_marks = ['good \nmental health', 'poor \nmental health']

may help as well.

3) Another way to improve the way you use space is to rotate the ylabels:

 plt.yticks(tick_marks, classes, size = 12, rotation='vertical')

You should try different combinations and see what happens.