Changing the rotation of tick labels in Seaborn heatmap

Question or problem about Python programming:

I’m plotting a heatmap in Seaborn. The problem is that I have too many squares in my plot so the x and y labels are too close to each other to be useful. So I’m creating a list of xticks and yticks to use. However passing this list to the function rotates the labels in the plot. It would be really nice to have seaborn automatically drop some of the ticks, but barring that I would like to be able to have the yticks upright.

import pandas as pd
import numpy as np
import seaborn as sns

data = pd.DataFrame(np.random.normal(size=40*40).reshape(40,40))

yticks = data.index
keptticks = yticks[::int(len(yticks)/10)]
yticks = ['' for y in yticks]
yticks[::int(len(yticks)/10)] = keptticks

xticks = data.columns
keptticks = xticks[::int(len(xticks)/10)]
xticks = ['' for y in xticks]
xticks[::int(len(xticks)/10)] = keptticks

sns.heatmap(data,linewidth=0,yticklabels=yticks,xticklabels=xticks)

How to solve the problem:

Solution 1:

seaborn uses matplotlib internally, as such you can use matplotlib functions to modify your plots. I’ve modified the code below to use the plt.yticks function to set rotation=0 which fixes the issue.

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


data = pd.DataFrame(np.random.normal(size=40*40).reshape(40,40))

yticks = data.index
keptticks = yticks[::int(len(yticks)/10)]
yticks = ['' for y in yticks]
yticks[::int(len(yticks)/10)] = keptticks

xticks = data.columns
keptticks = xticks[::int(len(xticks)/10)]
xticks = ['' for y in xticks]
xticks[::int(len(xticks)/10)] = keptticks

sns.heatmap(data,linewidth=0,yticklabels=yticks,xticklabels=xticks)

# This sets the yticks "upright" with 0, as opposed to sideways with 90.
plt.yticks(rotation=0) 

plt.show()

Solution 2:

You can also call the methods of heatmap object:

    g = sns.heatmap(data,linewidth=0,yticklabels=yticks,xticklabels=xticks)
    g.set_yticklabels(g.get_yticklabels(), rotation = 0, fontsize = 8)

I am not sure why this isn’t in the documentation for sns.heatmap, but the same methods are described here: http://seaborn.pydata.org/generated/seaborn.FacetGrid.html

I believe these methods are available to every seaborn plot object but couldn’t find a general API for that.

Hope this helps!