使用多色线向 matplotlib 图中添加图例

Question

按照有关如何绘制多色线的示例，我可以绘制基于某些颜色图沿其长度改变颜色的线。尝试向情节添加图例我添加了以下代码：

plt.legend([lc], ["test"],\
    handler_map={lc: matplotlib.legend_handler.HandlerLineCollection()})

这为绘图添加了一个图例（下图），但图例中图标的颜色与线条的颜色完全无关。这是尝试向该图添加图例的错误方法，还是 matplotlib 的限制？

Answer 1

这个想法也是在图例中显示一个线条集合。没有内置的方法可以做到这一点，但可以在其方法中HandlerLineCollection创建子类并创建相应LineCollection的create_artists方法。

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.legend_handler import HandlerLineCollection
from matplotlib.collections import LineCollection

class HandlerColorLineCollection(HandlerLineCollection):
    def create_artists(self, legend, artist ,xdescent, ydescent,
                        width, height, fontsize,trans):
        x = np.linspace(0,width,self.get_numpoints(legend)+1)
        y = np.zeros(self.get_numpoints(legend)+1)+height/2.-ydescent
        points = np.array([x, y]).T.reshape(-1, 1, 2)
        segments = np.concatenate([points[:-1], points[1:]], axis=1)
        lc = LineCollection(segments, cmap=artist.cmap,
                     transform=trans)
        lc.set_array(x)
        lc.set_linewidth(artist.get_linewidth())
        return [lc]

t = np.linspace(0, 10, 200)
x = np.cos(np.pi * t)
y = np.sin(t)
points = np.array([x, y]).T.reshape(-1, 1, 2)
segments = np.concatenate([points[:-1], points[1:]], axis=1)

lc = LineCollection(segments, cmap=plt.get_cmap('copper'),
                    norm=plt.Normalize(0, 10), linewidth=3)
lc.set_array(t)

fig, ax = plt.subplots()
ax.add_collection(lc)

plt.legend([lc], ["test"],\
    handler_map={lc: HandlerColorLineCollection(numpoints=4)}, framealpha=1)

ax.autoscale_view()
plt.show()