增加 matplotlib 中图例线的行宽

下面是一个简单的例子:

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()

If you want to change all lines in a plot, it might be useful to define your own legend handler:

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()

@Brendan Wood's method uses the api provided by pyplot. In matplotlib, the 首选使用轴的面向对象样式. The following is how you can achieve this using axes method.

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)')


# get the legend object
leg = ax.legend()


# change the line width for the legend
for line in leg.get_lines():
line.set_linewidth(4.0)


plt.show()

制作的情节如下所示,

默认情况下，图例包含行本身。因此，改变画布中线条的线宽也会改变图例中的线条(反之亦然，因为它们本质上是同一个对象)。

一个可能的解决方案是从画布上使用艺术家的拷贝，并且只改变拷贝的线宽。

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()

另一种选择是使用 handler_map和更新函数。这在某种程度上是自动的，指定处理程序映射将自动使图例中的任何线条宽度为7点。

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()

结果和上面一样。