Manually set color of points in legend

问题:

I'm making a scatter plot which looks like this:

(MWE at bottom of question)

As can be seen in the image above the colors of the points in the legend are set to blue automatically by matplotlib. I need to set this points to some other color not present in the colormap (ie: black) so they won't generate confusion with the colors associated with said colormap.

I looked around but the matplotlib.legend module does not seem to accept a color keyword. Is there any way to do this?

---

Here's the MWE:

import matplotlib.pyplot as plt
import numpy as np

def rand_data():
    return np.random.uniform(low=0., high=1., size=(100,))

# Generate data.
x, y, x2, x3 = [rand_data() for i in range(4)]
# This data defines the markes and labels used.
x1 = np.random.random_integers(7, 9, size=(100,))

# Order all lists so smaller points are on top.
order = np.argsort(-np.array(x2))
# Order x and y.
x_o, y_o = np.take(x, order), np.take(y, order)
# Order list related to markers and labels.
z1 = np.take(x1, order)
# Order list related to sizes.
z2 = np.take(x2, order)
# Order list related to colors.
z3 = np.take(x3, order)

plt.figure()
cm = plt.cm.get_cmap('RdYlBu')

# Scatter plot where each value in z1 has a different marker and label
# assigned.
mrk = {7: ('o', '7'), 8: ('s', '8'), 9: ('D', '9')}
for key, value in mrk.items():

    s1 = (z1 == key)
    plt.scatter(x_o[s1], y_o[s1], marker=value[0], label=value[1],
        s=z2[s1] * 100., c=z3[s1], cmap=cm, lw=0.2)

# Plot colorbar
plt.colorbar()

# Plot legend.
plt.legend(loc="lower left", markerscale=0.7, scatterpoints=1, fontsize=10)

plt.show()

回答1:

You can obtain the legend handles and change their colors doing:

ax = plt.gca()
leg = ax.get_legend()
leg.legendHandles[0].set_color('red')
leg.legendHandles[1].set_color('yellow')

回答2:

You can retrieve the label of each legend handle with lh.get_label() if you want to map colors to specific labels.

For my purposes it worked best to create a dict from legendHandles and change the colors like so:

ax = plt.gca()
leg = ax.get_legend()
hl_dict = {handle.get_label(): handle for handle in leg.legendHandles}
hl_dict['9'].set_color('red')
hl_dict['8'].set_color('yellow')