在matplotlib中增加圖例線條的線寬

Question

我知道如果我更改線條的線寬，那是在圖例中自動更新的。 但是我想在不影響繪圖的情況下更改圖例線寬。

Answer 1

下面是如何做到這一點簡單的例子：

import numpy as np 
import matplotlib.pyplot as plt 

# make some data 
x = np.linspace(0, 2*np.pi) 
y1 = np.sin(x) 
y2 = np.cos(x) 

# plot sin(x) and cos(x) 
p1 = plt.plot(x, y1, 'b-', linewidth=1.0) 
p2 = plt.plot(x, y2, 'r-', linewidth=1.0) 

# make a legend for both plots 
leg = plt.legend([p1, p2], ['sin(x)', 'cos(x)'], loc=1) 

# set the linewidth of each legend object 
for legobj in leg.legendHandles: 
    legobj.set_linewidth(2.0) 

plt.show() 

Answer 2

如果你想改變的所有行的情節，它可能是有用的，定義自己的傳奇處理程序：

import matplotlib.pyplot as plt 
from matplotlib import legend_handler 
from matplotlib.lines import Line2D 
import numpy as np 

class MyHandlerLine2D(legend_handler.HandlerLine2D): 
    def create_artists(self, legend, orig_handle, 
         xdescent, ydescent, width, height, fontsize, 
         trans): 

     xdata, xdata_marker = self.get_xdata(legend, xdescent, ydescent, 
              width, height, fontsize) 

     ydata = ((height-ydescent)/2.)*np.ones(xdata.shape, float) 
     legline = Line2D(xdata, ydata) 

     self.update_prop(legline, orig_handle, legend) 
     #legline.update_from(orig_handle) 
     #legend._set_artist_props(legline) # after update 
     #legline.set_clip_box(None) 
     #legline.set_clip_path(None) 
     legline.set_drawstyle('default') 
     legline.set_marker("") 
     legline.set_linewidth(10) 


     legline_marker = Line2D(xdata_marker, ydata[:len(xdata_marker)]) 
     self.update_prop(legline_marker, orig_handle, legend) 
     #legline_marker.update_from(orig_handle) 
     #legend._set_artist_props(legline_marker) 
     #legline_marker.set_clip_box(None) 
     #legline_marker.set_clip_path(None) 
     legline_marker.set_linestyle('None') 
     if legend.markerscale != 1: 
      newsz = legline_marker.get_markersize()*legend.markerscale 
      legline_marker.set_markersize(newsz) 
     # we don't want to add this to the return list because 
     # the texts and handles are assumed to be in one-to-one 
     # correpondence. 
     legline._legmarker = legline_marker 

     return [legline, legline_marker] 


plt.plot([0, 1], [0, 1], '-r', lw=1, label='Line') 
plt.legend(handler_map={Line2D:MyHandlerLine2D()}) 

plt.show() 

Answer 3

@Brendan Wood的方法使用pyplot提供的api。在matplotlib中，object oriented style using axes is prefered。以下是如何使用axes方法實現此目的。

import numpy as np 
import matplotlib.pyplot as plt 

# make some data 
x = np.linspace(0, 2*np.pi) 
y1 = np.sin(x) 
y2 = np.cos(x) 

fig, ax = plt.subplots() 
ax.plot(x, y1, linewidth=1.0, label='sin(x)') 
ax.plot(x, y2, linewidth=1.0, label='cos(x)') 
leg = ax.legend() 

for line in leg.get_lines(): 
    line.set_linewidth(4.0) 

plt.show() 

所產生的曲線圖顯示如下，

Answer 4

默認情況下，圖例包含線本身。因此，更改畫布中線條的線寬也會更改圖例中的線條（反之亦然，因爲它們本質上是同一個對象）。

一個可能的解決方案是從畫布中使用藝術家的副本，並僅更改副本的線寬。

import numpy as np 
import matplotlib.pyplot as plt 
import copy 

x = np.linspace(0, 2*np.pi) 
y1 = np.sin(x) 
y2 = np.cos(x) 
fig = plt.figure() 
ax = fig.add_subplot(111) 
ax.plot(x, y1, c='b', label='y1',linewidth=1.0) 
ax.plot(x, y2, c='r', label='y2') 

# obtain the handles and labels from the figure 
handles, labels = ax.get_legend_handles_labels() 
# copy the handles 
handles = [copy.copy(ha) for ha in handles ] 
# set the linewidths to the copies 
[ha.set_linewidth(7) for ha in handles ] 
# put the copies into the legend 
leg = plt.legend(handles=handles, labels=labels) 

plt.savefig('leg_example') 
plt.show() 

不同的選擇將是使用一個handler_map和更新功能。這在某種程度上是自動的，指定處理程序貼圖會自動使圖例中的任何一行變爲7點寬。

import numpy as np 
import matplotlib.pyplot as plt 
from matplotlib.legend_handler import HandlerLine2D 

x = np.linspace(0, 2*np.pi) 
y1 = np.sin(x) 
y2 = np.cos(x) 
fig = plt.figure() 
ax = fig.add_subplot(111) 
ax.plot(x, y1, c='b', label='y1',linewidth=1.0) 
ax.plot(x, y2, c='r', label='y2') 

linewidth=7 
def update(handle, orig): 
    handle.update_from(orig) 
    handle.set_linewidth(7) 

plt.legend(handler_map={plt.Line2D : HandlerLine2D(update_func=update)}) 

plt.show() 

結果與上面相同。