How to use both fixed colors and colorbar with range in matplotlib/seaborn heatmap

Question

I saw JohanC's answer here:

How to set fixed color ranges with Seaborn heatmap?

When I made my plot, I had two types of cells that I needed to highlight: those with fixed values (e.g.,0 and 1), and those that varied within a range (e.g., 9-200). For the first type, fixed colors look nice. For the second type, a standard colorbar looks nice. Is there a way to have both, i.e., specify a set of cells to conditionally use fixed colors and if they go above a certain value, use a colorbar to color them?

Thanks, Michael

Regular colorbar example

sns.heatmap(np.clip(np.random.rand(21, 12) - 0.1, 0, 1)*100)
plt.show()

mozway · Accepted Answer · 2025-08-04 11:29:08Z

1

The most straightforward might be to use the mask in heatmap to plot the two cmaps independently:

from matplotlib.colors import BoundaryNorm, ListedColormap
import seaborn as sns

# example
np.random.seed(0)
data = np.clip(np.random.rand(21, 12)*1.2 - 0.1, 0, 1)*100

# identify values to mask (here 0 and 100)
mask = (data == 0) | (data == 100)

# plot fixed values
cmap = ListedColormap(['green', 'blue'])
norm = BoundaryNorm([0, 50, 100], len(cmap.colors))
ax = sns.heatmap(data, mask=~mask, cmap=cmap, norm=norm)

# plot the rest
sns.heatmap(data, mask=mask, ax=ax)

Output:

answered Aug 4 at 11:29

mozway

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