Lines to separate groups in seaborn heatmap

Question

I am plotting data as a Seaborn heatmap in Python. My data is intrinsically grouped into categories, and I'd like to have lines on the plot to indicate where the groups lie on the map. As a simple example, suppose I wanted to modify this plot from the documentation...

import seaborn as sns; sns.set()
flights = sns.load_dataset("flights")
flights = flights.pivot("month", "year", "passengers")
ax = sns.heatmap(flights, cbar=False)

Where I wanted to emphasize the comparisons between quarters of the year by making a plot like the one below; how would I do that?

Solution

You want ax.hlines:

ax.hlines([3, 6, 9], *ax.get_xlim())

Comments

[T. Carson]

I figured there had to be a simple answer; drives me nuts when I can't find it. Thank you so much. :)

[mwaskom]

ax.axhline will avoid having to specify the x limits of the line, but you'll have to call it multiple times.

[ilyas]

@Goyo Is there a way to separate the heatmap at certain locations. So I do not want to draw a line, but rather separate by a tiny distance, think of it as creating islands.

[Stop harming Monica]

@ilyas I don't think so but you can slice the data and plot to several subplots.