CODEWITHSUNDEEP
pythonmatplotliblegend
user2171215
user2171215

Reputation:

How to define a single legend for a set of subplots on matplotlib?

This may seem like a duplicate, but I swear I tried to find a compatible answer.

I have a set of histograms of different properties of the same 3 samples. So I want a legend with the name of these tree samples.

I tried defining the same labels('h1','h2' and 'h3') in all histograms, like this:

plt.subplot(121)
plt.hist(variable1[sample1], histtype = 'step', normed = 'yes', label = 'h1')
plt.hist(variable1[sample2], histtype = 'step', normed = 'yes', label = 'h2')
plt.hist(variable1[sample3], histtype = 'step', normed = 'yes', label = 'h3')

plt.subplot(122)
plt.hist(variable2[sample1], histtype = 'step', normed = 'yes', label = 'h1')
plt.hist(variable2[sample2], histtype = 'step', normed = 'yes', label = 'h2')
plt.hist(variable2[sample3], histtype = 'step', normed = 'yes', label = 'h3')

Then I used:

plt.legend( ['h1', 'h2', 'h3'], ['Name Of Sample 1', 'Name Of Sample 2', 'Name Of Sample 3'],'upper center')

The legend appears, but is empty. Any ideas?

Upvotes: 1

Views: 361

Answers (1)

tacaswell
tacaswell

Reputation: 87356

You have two problems. The first is that you are misunderstanding what label does. It does not mark the artists to be accessed via that name, but provides the text used by legend if you call legend with out any arguments. The second problem is that bar does not have an auto-generated legend handler.

fig, (ax1, ax2) = plt.subplots(1, 2)

h1 = ax1.hist(variable1[sample1], histtype='step', normed='yes', label='h1')
h2 = ax1.hist(variable1[sample2], histtype='step', normed='yes', label='h2')
h3 = ax1.hist(variable1[sample3], histtype='step', normed='yes', label='h3')

ha = ax2.hist(variable2[sample1], histtype='step', normed='yes', label='h1')
hb = ax2.hist(variable2[sample2], histtype='step', normed='yes', label='h2')
hc = ax2.hist(variable2[sample3], histtype='step', normed='yes', label='h3')

# this gets the line colors from the first set of histograms and makes proxy artists
proxy_lines = [matplotlib.lines.Line2D([], [], color=p[0].get_edgecolor()) for (_, _, p) in [h1, h2, h3]]

fig.legend(proxy_lines, ['label 1', 'label 2', 'label 3'])

also see http://matplotlib.org/users/legend_guide.html#using-proxy-artist

Upvotes: 1

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