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263 lines
95 KiB
Markdown
263 lines
95 KiB
Markdown
# 标签
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In [1]:
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```py
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import numpy as np
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import matplotlib as mpl
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import matplotlib.pyplot as plt
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%matplotlib inline
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```
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`legend()` 函数被用来添加图像的标签，其主要相关的属性有：
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* legend entry - 一个 legend 包含一个或多个 entry，一个 entry 对应一个 key 和一个 label
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* legend key - marker 的标记
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* legend label - key 的说明
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* legend handle - 一个 entry 在图上对应的对象
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## 使用 legend
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调用 `legend()` 会自动获取当前的 `Axes` 对象，并且得到这些 handles 和 labels，相当于：
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```py
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handles, labels = ax.get_legend_handles_labels()
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ax.legend(handles, labels)
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```
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我们可以在函数中指定 `handles` 的参数：
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In [2]:
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```py
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line_up, = plt.plot([1,2,3], label='Line 2')
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line_down, = plt.plot([3,2,1], label='Line 1')
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plt.legend(handles=[line_up, line_down])
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plt.show()
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```
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可以将 labels 作为参数输入 `legend` 函数：
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In [3]:
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```py
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line_up, = plt.plot([1,2,3])
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line_down, = plt.plot([3,2,1])
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plt.legend([line_up, line_down], ['Line Up', 'Line Down'])
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plt.show()
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```
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## 产生特殊形状的 marker key
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有时我们可以产生一些特殊形状的 marker：
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块状：
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In [4]:
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```py
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import matplotlib.patches as mpatches
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red_patch = mpatches.Patch(color='red', label='The red data')
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plt.legend(handles=[red_patch])
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plt.show()
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```
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点线组合：
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In [5]:
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```py
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import matplotlib.lines as mlines
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import matplotlib.pyplot as plt
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blue_line = mlines.Line2D([], [], color='blue', marker='*',
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markersize=15, label='Blue stars')
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plt.legend(handles=[blue_line])
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plt.show()
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```
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## 指定 legend 的位置
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`bbox_to_anchor` 关键词可以指定 `legend` 放置的位置，例如放到图像的右上角：
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In [6]:
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```py
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plt.plot([1,2,3], label="test1")
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plt.plot([3,2,1], label="test2")
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plt.legend(bbox_to_anchor=(1, 1),
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bbox_transform=plt.gcf().transFigure)
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plt.show()
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```
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更复杂的用法：
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In [7]:
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```py
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plt.subplot(211)
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plt.plot([1,2,3], label="test1")
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plt.plot([3,2,1], label="test2")
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# Place a legend above this legend, expanding itself to
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# fully use the given bounding box.
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plt.legend(bbox_to_anchor=(0., 1.02, 1., .102), loc=3,
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ncol=2, mode="expand", borderaxespad=0.)
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plt.subplot(223)
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plt.plot([1,2,3], label="test1")
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plt.plot([3,2,1], label="test2")
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# Place a legend to the right of this smaller figure.
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plt.legend(bbox_to_anchor=(1.05, 1), loc=2, borderaxespad=0.)
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plt.show()
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```
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## 同一个 Axes 中的多个 legend
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可以这样添加多个 `legend`：
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In [8]:
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```py
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line1, = plt.plot([1,2,3], label="Line 1", linestyle='--')
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line2, = plt.plot([3,2,1], label="Line 2", linewidth=4)
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# Create a legend for the first line.
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first_legend = plt.legend(handles=[line1], loc=1)
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# Add the legend manually to the current Axes.
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ax = plt.gca().add_artist(first_legend)
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# Create another legend for the second line.
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plt.legend(handles=[line2], loc=4)
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plt.show()
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```
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其中 `loc` 参数可以取 0-10 或者 字符串，表示放置的位置：
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| loc string | loc code |
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| --- | --- |
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| `'best'` | 0 |
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| `'upper right'` | 1 |
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| `'upper left'` | 2 |
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| `'lower left'` | 3 |
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| `'lower right'` | 4 |
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| `'right'` | 5 |
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| `'center left'` | 6 |
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| `'center right'` | 7 |
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| `'lower center'` | 8 |
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| `'upper center'` | 9 |
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| `'center'` | 10 |
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## 更多用法
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多个 `handle` 可以通过括号组合在一个 entry 中：
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In [9]:
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```py
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from numpy.random import randn
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z = randn(10)
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red_dot, = plt.plot(z, "ro", markersize=15)
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# Put a white cross over some of the data.
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white_cross, = plt.plot(z[:5], "w+", markeredgewidth=3, markersize=15)
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plt.legend([red_dot, (red_dot, white_cross)], ["Attr A", "Attr A+B"])
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plt.show()
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```
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自定义 `handle`：
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In [10]:
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```py
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import matplotlib.pyplot as plt
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import matplotlib.patches as mpatches
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class AnyObject(object):
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pass
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class AnyObjectHandler(object):
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def legend_artist(self, legend, orig_handle, fontsize, handlebox):
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x0, y0 = handlebox.xdescent, handlebox.ydescent
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width, height = handlebox.width, handlebox.height
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patch = mpatches.Rectangle([x0, y0], width, height, facecolor='red',
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edgecolor='black', hatch='xx', lw=3,
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transform=handlebox.get_transform())
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handlebox.add_artist(patch)
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return patch
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plt.legend([AnyObject()], ['My first handler'],
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handler_map={AnyObject: AnyObjectHandler()})
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plt.show()
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```
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椭圆：
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In [11]:
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```py
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from matplotlib.legend_handler import HandlerPatch
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import matplotlib.pyplot as plt
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import matplotlib.patches as mpatches
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class HandlerEllipse(HandlerPatch):
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def create_artists(self, legend, orig_handle,
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xdescent, ydescent, width, height, fontsize, trans):
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center = 0.5 * width - 0.5 * xdescent, 0.5 * height - 0.5 * ydescent
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p = mpatches.Ellipse(xy=center, width=width + xdescent,
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height=height + ydescent)
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self.update_prop(p, orig_handle, legend)
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p.set_transform(trans)
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return [p]
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c = mpatches.Circle((0.5, 0.5), 0.25, facecolor="green",
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edgecolor="red", linewidth=3)
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plt.gca().add_patch(c)
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plt.legend([c], ["An ellipse, not a rectangle"],
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handler_map={mpatches.Circle: HandlerEllipse()})
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plt.show()
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```
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