How to set alpha of the fill area in violinplot? param alpha seems not work.

[CCHLENG]

Hi, I am drawing a violinplot by seaborn. I want to set the fill area as alpha=0.5 and edge(edge line) alpha=1.

However, I found that the param alpha and color not work.

When I use sns.violinplot(data=[data], color=(1, 0, 0), alpha=0.5) or sns.violinplot(data=[data], color=(1, 0, 0, 0.5)) , I get same figure:

Then I tried folowing code:

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

data = np.random.normal(loc=0, scale=1, size=100)

ax = sns.violinplot(data=[data], color=(1, 0, 0))

for patch in ax.collections:
    patch.set_alpha(0.5)

plt.show()

It works, I get this figure. But the alpha of the edge(edge line) is also set as 0.5.

So how can set only the fill area as alpha=0.5? Thanks!

[thuiop]

Pretty sure that matplotlib does not support different alpha for the fill and edge colors ; nothing much to do here (except reaching down to matplotlib if you really need it). Also alpha is not supposed to be a parameter of violinplot which is why it does not work, though I suppose it could be added. I am not sure of the use case though as you would not expect them to be stacked.

[CCHLENG]

Thank you! Sometimes I can need to stack violin plots in order to compare the distribution of data. Now I set the alpha of the fill manually by saving the image in svg through adobe. Fortunately, the fill and contour lines are on different layers.

[mwaskom]

You can pass an alpha value to fillcolor

sns.violinplot(data=[data], facecolor=(1, 0, 0, .2), linewidth=3)

[CCHLENG]

It works! Thank you very much!