seaborn heatmap not displaying correctly

Question

For some reason, my heatmap is not displaying correctly anymore. It was working just fine even with 6 classes. Since the last time I used it, I've installed many packages (including plotly). I don't know what exactly has caused this. How can I make the annotations and the x/y labels centered again? In both images the exact same code is used.

    import matplotlib.pyplot as plt
    import seaborn
    conf_mat = confusion_matrix(valid_y, y_hat)
    fig, ax = plt.subplots(figsize=(8,6))
    seaborn.heatmap(conf_mat, annot=True, fmt='d',xticklabels=classes, yticklabels=classes)
    plt.ylabel('Actual')
    plt.xlabel('Predicted')
    plt.show()

Answer 1

Current version of matplotlib broke heatmaps. Downgrade the package to 3.1.0

pip install matplotlib==3.1.0

matplotlib/seaborn: first and last row cut in half of heatmap plot

Answer 2

I had the same problem, solved by moving y axis:

ax.set_ylim([0,2])

Answer 3

You can work around this without downgrading, if you offset the ticks.

For a $2\times2$ matrix, this works:

fig, ax = plt.subplots()
cm = confusion_matrix(labels, predictions)

im = ax.imshow(cm, interpolation='nearest', cmap=plt.cm.Blues)
ax.figure.colorbar(im, ax=ax)

ax.set(yticks=[-0.5, 1.5], 
       xticks=[0, 1], 
       yticklabels=classes, 
       xticklabels=classes)
# ax.yaxis.set_major_locator(ticker.IndexLocater(base=1, offset=0.5))
# should change to 
ax.yaxis.set_major_locator(ticker.IndexLocator(base=1, offset=0.5))

Answer 4

plot confusion matrix by using seaborn library

tn, fp, fn, tp = metrics.confusion_matrix(y_test,y_pred).ravel()
matrix = np.array([[tp,fp],[fn,tn]])

# plot 
sns.heatmap(matrix,annot=True, cmap="viridis" ,fmt='g')
plt.xticks([0.5,1.5],labels=[1,0])
plt.yticks([0.5,1.5],labels=[1,0])
plt.title('Confusion matrix')
plt.xlabel('Actual label')
plt.ylabel('Predicted label');