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matplotlib学习笔记_python培训

python培训 cdadata 1394℃

matplotlib学习笔记_matlab培训

legend 显示图例

1 legend基础

函数原型 legend(*args, **kwargs) 

len(args) == 2

       args 是[artist][label]的集合

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LineCollectionor 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])

 

matplotlib学习笔记_matlab培训

# or sort them by labels

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

handles2, labels2 = zip(*hl)

ax.legend(handles2, labels2)

matplotlib学习笔记_matlab培训

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”)

 

matplotlib学习笔记_matlab培训

 

 

3 图例位置

 

ax.legend(., loc=3) 具体对应位置如下图

matplotlib学习笔记_matlab培训

绘制在图上是这样的,(具体没有分清 57的区别)

matplotlib学习笔记_matlab培训

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;0.775×0.8)

handles — 图例上面画出的各个artistlines, 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

matplotlib学习笔记_matlab培训

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 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 in leg.get_lines():

    l.set_linewidth(1.5)  # the legend line width

 

matplotlib学习笔记_matlab培训

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’)

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