matplotlib - making labels for violin plots

Question

I usually make labels for bars in the following manner using parameter 'label' in the method 'bar'.

axes[0].bar(x, y, bar_width, label='abc')
axes[0].legend()

Now I'd like to plot violin plots and make label for each collection as follows, but it doesn't work since 'violinplot' doesn't have the parameter 'label'.

axes[0].violinplot(data1, label='abc1')
axes[1].violinplot(data2, label='abc2')

Can anyone help me out to make a label for each collection?

Answer 1

Here is my solution for multple violin plots. Note that it grabs the patch color from the first shaded area of the given violin plot---this could be changed to do something else if there are multiple colors, or you could instead grab the color of the vertical bar with violin["cbars"].get_color().flatten().

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
import numpy as np

labels = []
def add_label(violin, label):
    color = violin["bodies"][0].get_facecolor().flatten()
    labels.append((mpatches.Patch(color=color), label))


positions = np.arange(3,13,3)
data = np.random.randn(1000, len(positions))
add_label(plt.violinplot(data, positions), "Flat")    

positions = np.arange(1, 10, 2)
data = np.random.randn(1000, len(positions)) + positions
add_label(plt.violinplot(data, positions), "Linear")

positions = np.arange(2, 11, 1)
data = np.random.randn(1000, len(positions)) + positions ** 2 / 4
add_label(plt.violinplot(data, positions), "Quadratic")

plt.legend(*zip(*labels), loc=2)

Answer 2

edit: sorry, I now see that you wanted to add a legend, not axis labels...

You can manually set the tick locations and then overwrite their labels:

import numpy as np
import matplotlib.pyplot as pl

pos   = [1, 2, 4, 5, 7, 8]
label = ['abc','def','ghi','jkl','mno','pqr']
data  = [np.random.normal(size=100) for i in pos]

pl.figure()
ax = pl.subplot(111)
pl.violinplot(data, pos, vert=False)
ax.set_yticks(pos)
ax.set_yticklabels(label)