Matplotlib：如何绘制一个填充有颜色图的小矩形作为图例

Question

而不是在我的情节旁边绘制一个颜色条，我想绘制一个填充颜色图的小矩形作为图例。

通过执行以下技巧，我已经可以绘制一个填充任何颜色的小矩形：

axis0, = myax.plot([], linewidth=10, color='r')

axis =[axis0]
legend=['mytext']

plt.legend(axis,
           legend)

我可以对颜色图做同样的事情吗？谢谢！

Answer 1

据我所知，除了从头开始创建矩形和图例之外，没有其他方法可以做到这一点。这是一种方法（主要基于这个答案）：

import numpy as np                                    # v 1.19.2
import matplotlib.pyplot as plt                       # v 3.3.2
import matplotlib.patches as patches
from matplotlib.legend_handler import HandlerTuple

rng = np.random.default_rng(seed=1)

ncmaps = 5     # number of colormaps to draw for illustration
ncolors = 100  # number high enough to draw a smooth gradient for each colormap

# Create random list of colormaps and extract list of colors to 
# draw the gradient of each colormap
cmaps_names = list(rng.choice(plt.colormaps(), size=ncmaps))
cmaps = [plt.cm.get_cmap(name) for name in cmaps_names]
cmaps_gradients = [cmap(np.linspace(0, 1, ncolors)) for cmap in cmaps]
cmaps_dict = dict(zip(cmaps_names, cmaps_gradients))

# Create a list of lists of patches representing the gradient of each colormap
patches_cmaps_gradients = []
for cmap_name, cmap_colors in cmaps_dict.items():
    cmap_gradient = [patches.Patch(facecolor=c, edgecolor=c, label=cmap_name)
                     for c in cmap_colors]
    patches_cmaps_gradients.append(cmap_gradient)

# Create custom legend (with a large fontsize to better illustrate the result)
plt.legend(handles=patches_cmaps_gradients, labels=cmaps_names, fontsize=20,
           handler_map={list: HandlerTuple(ndivide=None, pad=0)})

plt.show()

如果您计划对多个绘图执行此操作，您可能需要创建一个自定义图例处理程序，如此答案中所示。您可能还需要考虑显示颜色条的其他方式，例如此处、此处和此处所示的示例。

文档：图例指南