将项目添加到现有的Matplotlib图例 [英] Add item to existing Matplotlib legend

问题描述

进行以下设置:

from matplotlib import pyplot as plt
fig, ax = plt.subplots()
ax.plot([0,1,2,3,4,5,6], label='linear')
ax.plot([0,1,4,9,16,25,36], label='square')
lgd = ax.legend(loc='lower right')

如果函数add_patch仅接收lgd作为参数，是否可以将自定义图例项添加到现有项顶部的图例中，而无需更改图例的其他属性?

If a function add_patch receives only lgd as an argument, can a custom legend item be added to the legend on top of the existing items, without changing the other properties of the legend?

我可以使用以下方法添加项目:

I was able to add an item using:

def add_patch(legend):
    from matplotlib.patches import Patch
    ax = legend.axes
    handles, labels = ax.get_legend_handles_labels()
    handles.append(Patch(facecolor='orange', edgecolor='r'))
    labels.append("Color Patch")
    ax.legend(handles=handles, labels=labels)

但这不会保留图例之类的属性，例如location.绘制线条后，如何只给图例对象添加项目?

But this does not preserve the properties of the legend like location. How can I add an item given only the legend object after lines have been plotted?

推荐答案

原则上，图例不是要更新的，而是要重新创建的.

In principle a legend is not meant to be updated, but recreated instead.

以下内容将满足您的需求，但请注意，这是使用内部方法的黑客，因此不能保证能正常工作，并且可能在将来的发行版中破坏.因此，请勿在生产代码中使用它.另外，如果您为图例设置的标题使用的字体(大小)与默认字体不同，则更新后该标题将丢失.另外，如果您通过markerfirst操纵了手柄和标签的顺序，那么更新后该信息将丢失.

The following would do what you're after, but beware that this is a hack which uses internal methods and is hence not guaranteed to work and might break in future releases. So don't use it in production code. Also, if you have set a title to the legend with a different font(size) than default, it will be lost upon updating. Also, if you have manipulated the order of handles and labels via markerfirst, this will be lost upon updating.

from matplotlib import pyplot as plt
fig, ax = plt.subplots()
ax.plot([0,1,2,3,4,5,6], label='linear')
ax.plot([0,1,4,9,16,25,36], label='square')
lgd = ax.legend(loc='lower right')

def add_patch(legend):
    from matplotlib.patches import Patch
    ax = legend.axes

    handles, labels = ax.get_legend_handles_labels()
    handles.append(Patch(facecolor='orange', edgecolor='r'))
    labels.append("Color Patch")

    legend._legend_box = None
    legend._init_legend_box(handles, labels)
    legend._set_loc(legend._loc)
    legend.set_title(legend.get_title().get_text())


add_patch(lgd)

plt.show()

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