Add custom border to certain cells in a matplotlib / seaborn plot

Question

Right now I`m using Seaborn's clustermap to generate some clustered heatmaps - so far so good.

For a certain use case, I need to draw colored borders around specific cells. Is there a way to do that? Or with pcolormesh in matplotlib, or any other way?

Answer 1

You can do this by overplotting a Rectangle patch on the cell that you would want to highlight. Using the example plot from the seaborn docs

import seaborn as sns import matplotlib.pyplot as plt sns.set() flights = sns.load_dataset("flights") flights = flights.pivot("month", "year", "passengers") g = sns.clustermap(flights) 

We can highlight a cell by doing

from matplotlib.patches import Rectangle ax = g.ax_heatmap  ax.add_patch(Rectangle((3, 4), 1, 1, fill=False, edgecolor='blue', lw=3)) plt.show() 

This will produce the plot with a highlighted cell like so:

Note the the indexing of the cells is 0 based with the origin at the bottom left.