matplotlib学习笔记--Legend

legend 显示图例

1 legend基础

函数原型 legend(*args, **kwargs) 

当len(args) == 2

       args 是[artist]和[label]的集合

当len(args) == 0

       args会自动调用get_legend_handles_labels()生成

       等价于

       handles, labels = ax.get_legend_handles_labels()

      ax.legend(handles, labels)

ax.get_legend_handles_labels()的作用在于返回ax.lines, ax.patch所有对象以及ax.collection中的LineCollection or RegularPolyCollection对象

     注意：这里只提供有限支持, 并不是所有的artist都可以被用作图例，比如errorbar支持不完善

 

1.1 调整顺序

ax = subplot(1,1,1)

p1, = ax.plot([1,2,3], label="line 1")

p2, = ax.plot([3,2,1], label="line 2")

p3, = ax.plot([2,3,1], label="line 3")

handles, labels = ax.get_legend_handles_labels()

# reverse the order

ax.legend(handles[::-1], labels[::-1])

 

# or sort them by labels

import operator
hl = sorted(zip(handles, labels), key=operator.itemgetter(1))

handles2, labels2 = zip(*hl)

ax.legend(handles2, labels2)

1.2 使用代理artist

当需要使用legend不支持的artist时，可以使用另一个被legend支持的artist作为代理

比如以下示例中使用不在axe上的一个artist

p = Rectangle((0, 0), 1, 1, fc="r")

legend([p], ["Red Rectangle"])

 

2 多列图例

ax1 = plt.subplot(3,1,1)

ax1.plot([1], label="multi\nline")

ax1.plot([1], label="$2^{2^2}$")

ax1.plot([1], label=r"$\frac{1}{2}\pi$")

ax1.legend(loc=1, ncol=3, shadow=True)

 

ax2 = plt.subplot(3,1,2)

myplot(ax2)

ax2.legend(loc="center left", bbox_to_anchor=[0.5, 0.5],

           ncol=2, shadow=True, title="Legend")

ax2.get_legend().get_title().set_color("red")

 

 

 

3 图例位置

 

ax.legend(…., loc=3) 具体对应位置如下图

绘制在图上是这样的，（具体没有分清 5和7的区别）

4 多个图例

如果不采取措施，连续调用两个legend会使得后面的legend覆盖前面的

 

from matplotlib.pyplot import * p1, = plot([1,2,3], label="test1")

p2, = plot([3,2,1], label="test2")

l1 = legend([p1], ["Label 1"], loc=1)
l2 = legend([p2], ["Label 2"], loc=4) # this removes l1 from the axes.

gca().add_artist(l1) # add l1 as a separate artist to the axes

 

5. API

class matplotlib.legend.Legend(parent, handles, labels,**args)

三个最重要的必要参数

parent --- legend的父artist， 包含legend的对象

       比如用ax.legend()调用之后

       >>> print ax.get_legend().parent

       Axes(0.125,0.1;0.775x0.8)

handles --- 图例上面画出的各个artist（lines, patches）

labels --- artist 对应的标签

其他参数 

 

Keyword

Description

loc

a location code

prop

the font property (matplotlib.font_manager.FontProperties 对象)

eg

song_font = matplotlib.font_manager.FontProperties(fname='simsun.ttc', size=8)

fontsize

the font size (和prop互斥，不可同时使用)

markerscale

the relative size of legend markers vs. original

numpoints

the number of points in the legend for line

scatterpoints

the number of points in the legend for scatter plot

scatteryoffsets

a list of yoffsets for scatter symbols in legend

frameon

if True, draw a frame around the legend. If None, use rc

fancybox

if True, draw a frame with a round fancybox. If None, use rc

shadow

if True, draw a shadow behind legend

ncol

number of columns

borderpad

the fractional whitespace inside the legend border

labelspacing

the vertical space between the legend entries

handlelength

the length of the legend handles

handleheight

the length of the legend handles

handletextpad

the pad between the legend handle and text

borderaxespad

the pad between the axes and legend border

columnspacing

the spacing between columns

title

the legend title

bbox_to_anchor

the bbox that the legend will be anchored.

bbox_transform

the transform for the bbox. transAxes if None.

主要函数

get_frame() ---  返回legend所在的方形对象

get_lines()

get_patches()

get_texts()

get_title() ---  上面几个比较简单，不解释了

set_bbox_to_anchor(bbox, transform=None)

(…本函数待续…之后写axes的时候会加入，目前我没有看懂他的这个长宽和figure以及axes的关系)

 

6. 样例

leg = ax.legend(('Model length', 'Data length', 'Total message length'),

           'upper center', shadow=True)

# the matplotlib.patches.Rectangle instance surrounding the legend 即外框

frame  = leg.get_frame()

frame.set_facecolor('0.80')    # set the frame face color to light gray

 

# matplotlib.text.Text instances 即legend中文本

for t in leg.get_texts():

    t.set_fontsize('small')    # the legend text fontsize

 

# matplotlib.lines.Line2D instances 即legend中所表示的artist

for l in leg.get_lines():

    l.set_linewidth(1.5)  # the legend line width

 

fig = plt.figure()

ax1 = fig.add_axes([0.1, 0.1, 0.4, 0.7])

ax2 = fig.add_axes([0.55, 0.1, 0.4, 0.7])

 

x = np.arange(0.0, 2.0, 0.02)

y1 = np.sin(2*np.pi*x)

y2 = np.exp(-x)

l1, l2 = ax1.plot(x, y1, 'rs-', x, y2, 'go')

 

y3 = np.sin(4*np.pi*x)

y4 = np.exp(-2*x)

l3, l4 = ax2.plot(x, y3, 'yd-', x, y3, 'k^')

 

fig.legend((l1, l2), ('Line 1', 'Line 2'), 'upper left')

fig.legend((l3, l4), ('Line 3', 'Line 4'), 'upper right')