python画图matplotlib的Legend（显⽰图中的标签）legend(x, y = NULL, legend, fill = NULL, col = par("col"),
border ="black", lty, lwd, pch,
angle = 45,density = NULL, bty = "o", bg = par("bg"),
box.lwd = par("lwd"),box.lty = par("lty"), l = par("fg"),
pt.bg = NA, cex =1, pt.cex = cex, pt.lwd = lwd,
xjust = 0, yjust= 1, x.intersp = 1, y.intersp = 1,
adj = c(0, 0.5),text.width = NULL, l = par("col"),
text.font = NULL,merge = do.lines && has.pch, trace = FALSE,
plot = TRUE, ncol= 1, horiz = FALSE, title = NULL,
inset = 0, l = l, title.adj = 0.5,
seg.len = 2)
x, y X,y⽤于定位图例，也可⽤单键词"bottomright", "bottom", "bottomleft", "left", "topleft", "top", "topright", "right" and "center"
legend字符或表达式向量
fill⽤特定的颜⾊进⾏填充
col图例中出现的点或线的颜⾊
border当fill = 参数存在的情况下，填充⾊的边框
lty, lwd图例中线的类型与宽度
pch点的类型
angle阴影的⾓度
density阴影线的密度
bty图例框是否画出，o为画出，默认为n不画出
bg bty != "n"时，图例的背景⾊
box.lty, box.lwd,
bty = "o"时，图例框的类型，box.lty决定是否为虚线，box.lwd决定粗线，l决定颜⾊pt.bg点的背景⾊
cex字符⼤⼩
<点的⼤⼩
pt.lwd点的边缘的线宽
x.intersp图例中⽂字离图⽚的⽔平距离
y.intersp图例中⽂字离图⽚的垂直距离
adj图例中字体的相对位置
adj图例中字体的相对位置
text.width图例字体所占的宽度
text.font图例字体
merge logical, if TRUE，合并点与线，但不填充图例框，默认为TRUE
trace logical; if TRUE显⽰图例信息.
plot logical. If FALSE不画出图例
ncol图例中分类的列数
horiz logical; if TRUE,⽔平放置图例
title给图例加标题
inset当图例⽤关键词设置位置后，inset = 分数，可以设置其相对位置
xpd xpd=FALSE，即不允许在作图区域外作图，改为TRUE即可，与par()参数配合使⽤。l标题颜⾊
title.adj图例标题的相对位置，0.5为默认，在中间。0最左，1为最右。
seg.len lty 与lwd的线长，长度单位为字符宽度
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)
matplotlib中subplot
<_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")
<_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
>>> _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='', 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  = _frame()
frame.set_facecolor('0.80')    # set the frame face color to light gray
# Text instances即legend中⽂本
for t _texts():
t.set_fontsize('small')    # the legend text fontsize
# matplotlib.lines.Line2D instances即legend中所表⽰的artist
for l _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')
import matplotlib.patches as mpatches
import matplotlib.pyplot as plt
red_patch = mpatches.Patch(color='red', label='The red data') plt.legend(handles=[red_patch])
plt.show()
import matplotlib.lines as mlines
import matplotlib.pyplot as plt
blue_line = mlines.Line2D([], [], color='blue', marker='*',
markersize=15, label='Blue stars')
plt.legend(handles=[blue_line])
plt.show()
import matplotlib.pyplot as plt
plt.subplot(211)
plt.plot([1,2,3], label="test1")
plt.plot([3,2,1], label="test2")
# Place a legend above this subplot, expanding itself to
# fully use the given bounding box.
plt.legend(bbox_to_anchor=(0., 1.02, 1., .102), loc=3,
ncol=2, mode="expand", borderaxespad=0.)
plt.subplot(223)
plt.plot([1,2,3], label="test1")
plt.plot([3,2,1], label="test2")
# Place a legend to the right of this smaller subplot.
plt.legend(bbox_to_anchor=(1.05, 1), loc=2, borderaxespad=0.)
plt.show()
import matplotlib.pyplot as plt
line1, = plt.plot([1,2,3], label="Line 1", linestyle='--')
line2, = plt.plot([3,2,1], label="Line 2", linewidth=4)
# Create a legend for the first line.
first_legend = plt.legend(handles=[line1], loc=1)
# Add the legend manually to the current Axes.
ax = a().add_artist(first_legend)
# Create another legend for the second line.
plt.legend(handles=[line2], loc=4)
plt.show()
import matplotlib.pyplot as plt
from matplotlib.legend_handler import HandlerLine2D
line1, = plt.plot([3,2,1], marker='o', label='Line 1')
line2, = plt.plot([1,2,3], marker='o', label='Line 2')
plt.legend(handler_map={line1: HandlerLine2D(numpoints=4)})

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