Is it possible to have two different marker styles for a label in a Matplotlib legend?

Question

I want to customise a Matplotlib legend so that one of the labels is represented by two markers with different styles (e.g. ☆/▽ My label). I have seen that you can customise legend markers by making a patch for the marker, but can you create and use two patches (and at a push maybe add a "/" as a separator)? An option may also be to create a LaTeX string for the marker using TikZ, but that seems like overkill.

Answer 1

One way to do it would be to define custom markers using mathtext (see matplotlib documentation) and define the legend handle of the subclass with a proxy:

import numpy as np
import matplotlib.pyplot as plt

plt.close('all')

# Generate some data :

x1 = np.arange(1, 20)
y1 = np.log(x1) + np.random.uniform(-1, 1, size=len(x1))/5

x2 = np.arange(1, 20)
y2 = np.log(x2) + np.random.uniform(-1, 1, size=len(x2))/5

# Plot data :

fig, ax = plt.subplots()

h1, = ax.plot(x1[x1>5], y1[x1>5], ls='none', marker=r'$\star$',
              ms=12, mec='0.15', mfc='0.15', mew=1, alpha=0.5)

h2, = ax.plot(x2[x2>5], y2[x2>5], ls='none', marker=r'$\blacktriangledown$',
              ms=12, mec='0.15', mfc='0.15', mew=1, alpha=0.5)

ax.plot(x1[x1<=5], y1[x1<=5], ls='none', marker=r'$\star$',
        ms=12, mec='red', mfc='red', mew=1, alpha=0.5)

ax.plot(x2[x2<=5], y2[x2<=5], ls='none', marker=r'$\blacktriangledown$',
        ms=12, mec='red', mfc='red', mew=1, alpha=0.5)

# Create a proxy for the subclass :

h3, = ax.plot([], ls='none', marker=r'$\star/\blacktriangledown$',
              ms=24, mec='red', mfc='red', mew=1, alpha=0.5)


# Generate legend :

handles = [h1, h2, h3]
labels = ['dataset1', 'dataset2', 'transient state']
ax.legend(handles, labels, loc=4, ncol=1, numpoints=1, frameon=False)

# Save and show the figure :

fig.savefig('custom_legend_markers.png')
plt.show()