Table legend in matplotlib

问题:

I would like to make a complex legend in matplotlib. I made the following code

import matplotlib.pylab as plt
import numpy as np

N = 25
y = np.random.randn(N)
x = np.arange(N)

y2 = np.random.randn(25)

# serie A
p1a, = plt.plot(x, y,       "ro", ms=10, mfc="r", mew=2, mec="r")
p1b, = plt.plot(x[:5], y[:5] ,  "w+", ms=10, mec="w", mew=2) 
p1c, = plt.plot(x[5:10], y[5:10], "w*", ms=10, mec="w", mew=2) 

# serie B
p2a, = plt.plot(x, y2,       "bo", ms=10, mfc="b", mew=2, mec="b")
p2b, = plt.plot(x[15:20], y2[15:20] ,  "w+", ms=10, mec="w", mew=2) 
p2c, = plt.plot(x[10:15], y2[10:15], "w*", ms=10, mec="w", mew=2) 


plt.legend([p1a, p2a, (p1a, p1b), (p2a,p2b), (p1a, p1c), (p2a,p2c)], 
 ["No prop", "No prop", "Prop +", "Prop +", "Prop *", "Prop *"], ncol=3, numpoints=1)

plt.show()

It produces plot like that:

But I would like to plot complex legend like here:

I also tried to do the legend with table function but I can not put a patch object into the table to a proper position of a cell.

回答1:

Is this solution close enough to your liking? It is slighty inspired by Ricardo's answer, but I only used one legend-object for each column, and then utilised the title-keyword to set the title of each individual column. To put the markers in the center of each column I used handletextpad with a negative value to push it backward. There are no legends to individual lines. I also had to insert some spaces into the title-strings to make them look equally big when drawn on screen.

I also noticed now when the figure was saved that additional tweaks to the exact position of the legend-boxes and are needed, but since I guess you might want to tweak more stuff in the code anyway I leave it for you. You might also need to play yourself with the handletextpad to make them "perfectly" aligned.

import matplotlib.pylab as plt
import numpy as np
plt.close('all')

N = 25
y = np.random.randn(N)
x = np.arange(N)

y2 = np.random.randn(25)

# serie A
p1a, = plt.plot(x, y,       "ro", ms=10, mfc="r", mew=2, mec="r")
p1b, = plt.plot(x[:5], y[:5] ,  "w+", ms=10, mec="w", mew=2) 
p1c, = plt.plot(x[5:10], y[5:10], "w*", ms=10, mec="w", mew=2) 

# serie B
p2a, = plt.plot(x, y2,       "bo", ms=10, mfc="b", mew=2, mec="b")
p2b, = plt.plot(x[15:20], y2[15:20] ,  "w+", ms=10, mec="w", mew=2) 
p2c, = plt.plot(x[10:15], y2[10:15], "w*", ms=10, mec="w", mew=2) 

line_columns = [
                p1a, p2a,
                (p1a, p1b), (p2a, p2b),
                (p1a, p1c), (p2a, p2c)
                ]


leg1 = plt.legend(line_columns[0:2], ['', ''], ncol=1, numpoints=1, 
                  title='No prop', handletextpad=-0.4, 
                  bbox_to_anchor=[0.738, 1.])
leg2 = plt.legend(line_columns[2:4], ['', ''], ncol=1, numpoints=1, 
                  title=' Prop  + ', handletextpad=-0.4,
                  bbox_to_anchor=[0.87, 1.])
leg3 = plt.legend(line_columns[4:6], ['', ''], ncol=1, numpoints=1, 
                  title=' Prop  * ', handletextpad=-0.4, 
                  bbox_to_anchor=[0.99, 1.])

plt.gca().add_artist(leg1)
plt.gca().add_artist(leg2)
plt.gca().add_artist(leg3)

plt.gcf().show()

Edit

Maybe this will work better. You still have to tweak a few stuff, but the alignment-problem of the bboxes are away.

leg = plt.legend(line_columns, ['']*len(line_columns), 
             title='No Prop    Prop +    Prop *',  
             ncol=3, numpoints=1, handletextpad=-0.5)

回答2:

It seems there is no standard approach for this rather than some few tricks available over here.

It is worth mentioning that you should check the size bbox factor that fits you the most.

The best I could find so far, an perhaps can lead you to a better solution:

N = 25
y = np.random.randn(N)
x = np.arange(N)

y2 = np.random.randn(25)

# Get current size
fig_size = list(plt.rcParams["figure.figsize"])

# Set figure width to 12 and height to 9
fig_size[0] = 12
fig_size[1] = 12
plt.rcParams["figure.figsize"] = fig_size

# serie A
p1a, = plt.plot(x, y,       "ro", ms=10, mfc="r", mew=2, mec="r")
p1b, = plt.plot(x[:5], y[:5] ,  "w+", ms=10, mec="w", mew=2) 
p1c, = plt.plot(x[5:10], y[5:10], "w*", ms=10, mec="w", mew=2) 

# serie B
p2a, = plt.plot(x, y2,       "bo", ms=10, mfc="b", mew=2, mec="b")
p2b, = plt.plot(x[15:20], y2[15:20] ,  "w+", ms=10, mec="w", mew=2) 
p2c, = plt.plot(x[10:15], y2[10:15], "w*", ms=10, mec="w", mew=2) 

v_factor = 1.
h_factor = 1.

leg1 = plt.legend([(p1a, p1a)], ["No prop"], bbox_to_anchor=[0.78*h_factor, 1.*v_factor])
leg2 = plt.legend([(p2a, p2a)], ["No prop"], bbox_to_anchor=[0.78*h_factor, .966*v_factor])

leg3 = plt.legend([(p2a,p2b)], ["Prop +"], bbox_to_anchor=[0.9*h_factor, 1*v_factor])
leg4 = plt.legend([(p1a, p1b)], ["Prop +"], bbox_to_anchor=[0.9*h_factor, .966*v_factor])

leg5 = plt.legend([(p1a, p1c)], ["Prop *"], bbox_to_anchor=[1.*h_factor, 1.*v_factor])
leg6 = plt.legend([(p2a,p2c)], ["Prop *"], bbox_to_anchor=[1.*h_factor, .966*v_factor])

plt.gca().add_artist(leg1)
plt.gca().add_artist(leg2)
plt.gca().add_artist(leg3)
plt.gca().add_artist(leg4)
plt.gca().add_artist(leg5)
plt.gca().add_artist(leg6)
plt.show()

回答3:

I improve the answer of @pathoren to position legends automatically in a cycle according to bbox coordinate of legends. This code allow to show all desired border lines of a complex legend:

import matplotlib.pylab as plt
import numpy as np
plt.close('all')

# test data
N = 25
y = np.random.randn(N)
x = np.arange(N)
y2 = np.random.randn(25)

# serie A
p1a, = plt.plot(x, y, "ro", ms=10, mfc="r", mew=2, mec="r")
p1b, = plt.plot(x[:5], y[:5], "w+", ms=10, mec="w", mew=2) 
p1c, = plt.plot(x[5:10], y[5:10], "w*", ms=10, mec="w", mew=2) 
# serie B
p2a, = plt.plot(x, y2, "bo", ms=10, mfc="b", mew=2, mec="b")
p2b, = plt.plot(x[15:20], y2[15:20], "w+", ms=10, mec="w", mew=2) 
p2c, = plt.plot(x[10:15], y2[10:15], "w*", ms=10, mec="w", mew=2) 

# legend handlers
columns = [p1a, p2a, 
 (p1a, p1b), (p2a, p2b),
 (p1a, p1c), (p2a, p2c)]

ax = plt.gca()
fig = plt.gcf()
legs = []
# set the first legend in desired position
leg = plt.legend(columns[0:2], ['', ''], ncol=1, numpoints=1, 
 borderaxespad=0., title='No prop.', framealpha=.75,
 facecolor='w', edgecolor='k', loc=2, fancybox=None)
ax.add_artist(leg)
fig.canvas.draw()
plt.pause(1.e-3)

# get bbox postion of 1st legend to calculate
# postion of 2nd and 3rd legends according to loc
for i,si in enumerate(['+','*']):
    bbox = leg.get_window_extent().inverse_transformed(ax.transAxes)
    # next legends
    leg = plt.legend(columns[(i+1)*2:(i+1)*2+2], ['', ''], ncol=1, numpoints=1, 
     title='Prop. '+si, framealpha=.75, borderaxespad=.0,
     bbox_to_anchor=(bbox.x1-bbox.height*.08, bbox.y0, bbox.width, bbox.height),
     facecolor='w', edgecolor='k')
    ax.add_artist(leg)
    fig.canvas.draw()
    plt.pause(1.e-3)

plt.show()