Matplotlib: Multiple legends for contour plot for multiple contour variables

问题:

I need to make multiple contours plots of several variables on the same page. I can do this with MATLAB (see below for MATLAB code). I cannot get matplotlib to show multiple legends. Any help would be much appreciated.

Python code:

import numpy as np from matplotlib import cm as cm from matplotlib import pyplot as plt  delta = 0.25 x = np.arange(-3.0, 3.0, delta) y = np.arange(-2.0, 2.0, delta) X, Y = np.meshgrid(x, y) Z1 = X*np.exp(-X**2-Y**2) Z2 = Y*np.exp(-X**2-Y**2)  plt.figure() CS = plt.contour(X, Y, Z1, colors='k') plt.clabel(CS, inline=1, fontsize=10) CS = plt.contour(X, Y, Z2, colors='r') plt.clabel(CS, inline=1, fontsize=10) plt.legend(['case 1', 'case 2'])  plt.show() 

MATLAB code:

[X,Y] = meshgrid(-2:.2:2,-2:.2:3); Z1 = X.*exp(-X.^2-Y.^2); Z2 = Y.*exp(-X.^2-Y.^2);  [C,h] = contour(X,Y,Z1, 'color', 'k'); set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2); hold on  [C,h] = contour(X,Y,Z2, 'color', 'r'); set(h,'ShowText','on','TextStep',get(h,'LevelStep')*2);  fn = {'case 1', 'case 2'};  legend(fn,'Location','NorthWest'); 

回答1:

It would help if you showed your desired output from Matlab. For example, do you really want multiple legends? Or do you actually mean 1 legend with muliple items?

Since contour plots (can) have a different style for each level, its not obvious how you would want to plot that in a legend. But to get you started, you can access each individual line by examining the CS.collections array.

So for example:

delta = 0.25 x = np.arange(-3.0, 3.0, delta) y = np.arange(-2.0, 2.0, delta) X, Y = np.meshgrid(x, y) Z1 = X*np.exp(-X**2-Y**2) Z2 = Y*np.exp(-X**2-Y**2)  fig, ax = plt.subplots()  CS1 = ax.contour(X, Y, Z1, colors='k') ax.clabel(CS1, inline=1, fontsize=10)  CS2 = ax.contour(X, Y, Z2, colors='r') ax.clabel(CS2, inline=1, fontsize=10)  lines = [ CS1.collections[0], CS1.collections[-1], CS2.collections[0], CS2.collections[-1]] labels = ['CS1_neg','CS1_pos','CS2_neg','CS2_pos']  plt.legend(lines, labels) 

Results in:

Perhaps something like plt.legend(CS2.legend_elements()[0], CS2.legend_elements()[1]), can also be useful for you.

文章来源: Matplotlib: Multiple legends for contour plot for multiple contour variables