Does boxplot support alpha / transparency?

[amelio-vazquez-reina]

The following:

sns.boxplot(data, x='foo', y='bar', alpha=0.3)

Fails with:

TypeError: boxplot() got an unexpected keyword argument 'alpha'

I presume boxplots don't support alpha or transparency? Or is there any other way of getting it?

[amelio-vazquez-reina]

The above is using 0.7.0 on Python 3.5.2 (conda install on the default channel)

[mwaskom]

It's not supported through the seaborn API, but it is through kwargs that are passed down to matplotlib:

ax = sns.boxplot(x='day', y='tip', data=tips, boxprops=dict(alpha=.3))

But this also sets the alpha on the edges of the boxes, which I find aesthetically displeasing. A more roundabout way to grab the patch artists after plotting and then to just change the alpha of the box fills:

ax = sns.boxplot(x='day', y='tip', data=tips)
for patch in ax.artists:
    fc = patch.get_facecolor()
    patch.set_facecolor(mpl.colors.to_rgba(fc, 0.3))

there may be a more direct but less obvious way to do that, usually is in matplotlib.

[amelio-vazquez-reina]

Fantastic. Thanks @mwaskom !

[vinisalazar]

If you're trying to do this in 2022, change ax.artists for ax.patches, like so:

ax = sns.boxplot(x='day', y='tip', data=tips)
for patch in ax.patches:
    r, g, b, a = patch.get_facecolor()
    patch.set_facecolor((r, g, b, .3))

[mwaskom]

Specifically, that is a change in matplotlib 3.5.0. If you are using an older matplotlib in 2022, you should still do it the other way :)