Vfrdtyky

Edit: FWIW I am fixing the legend in Illustrator, but would prefer to do it automatically because I have about 20 of these plots to make

I followed this very helpful answer for adding a custom legend to a matplotlib violinplot, which doesn't support its own legend. It worked great except when I tried to add hatches.

Here's my code for the labels (I tried adding patch two different ways):

    labels = [ 'Low entropy bin', 'Medium entropy bin', 'High entropy bin' ]

    legend_patches = 3*[matplotlib.patches.Patch( color='#DCDCDC', hatch='//' )]

    for i in legend_patches:

       i.set_hatch( '//' )

The code for hatching the violins themselves works fine:

parts = plt.violinplot( data, showmeans=False, showextrema=True, showmedians=True )



hatch_dict = { 0:'', 1:'///', 2:'xx' }



for t in range(0, 3):

    third = range( 0, len( labels ) )[ t*(int(len(labels)/3)):(((t+1)*int(len(labels)/3))) ]

    for i in third:

        face = parts['bodies'][i]

        face.set_hatch( hatch_dict[t] )

The data the bins relate to (not shown) is already color coded for other categories so I'd really like to show the bins in different hatches.

You are almost there - just need to be careful with the color argument with patches. There are two sub-components: an edge (edgecolor) and a face (facecolor); with this patch artist setting the color= defines both of these colors. The hatch and the background then come out the same color and you can't see one from the other.

Bottom line: use something like this for your patch constructor:

p = matplotlib.patches.Patch(facecolor='#DCDCDC', hatch=hatch_dict[i])

Full code for this plot:

import numpy as np

import matplotlib.pyplot as plt

import matplotlib.patches



# generate some data

n = 50

sigmas = np.array([0.1, 0.05, 0.15])

means  = np.array([0.2, 0.5, 0.75])

data = sigmas * np.random.randn(n, 3) + means



labels = [ 'Low entropy bin', 'Medium entropy bin', 'High entropy bin' ]



parts = plt.violinplot( data, showmeans=False, showextrema=True, showmedians=True)



# set up color and hatching on the violins

hatch_dict = { 0:'', 1:'///', 2:'xx' }

for i, face in enumerate(parts['bodies']):

    face.set_hatch(hatch_dict[i])

    face.set_facecolor('#DCDCDC')



# for completeness update all the lines (you already had this styling applied)

for elem in ['cbars', 'cmedians', 'cmaxes', 'cmins']:

    parts[elem].set_edgecolor('0.5')



# construct proxy artist patches

leg_artists = 

for i in xrange(len(hatch_dict)):

    p = matplotlib.patches.Patch(facecolor='#DCDCDC', hatch=hatch_dict[i])

    # can also explicitly declare 2nd color like this

    #p = matplotlib.patches.Patch(facecolor='#DCDCDC', hatch=hatch_dict[i], edgecolor='0.5')



    leg_artists.append(p)



# and add them to legend.

ax = plt.gca()

ax.legend(leg_artists, labels, loc='upper left')