双y轴坐标轴图

今天利用matplotlib绘图，想要完成一个双坐标格式的图。

fig=plt.figure(figsize=(20,15))
ax1=fig.add_subplot(111)
ax1.plot(demo0719['TPS'],'b-',label='TPS',linewidth=2)
ax2=ax1.twinx()#这是双坐标关键一步
ax2.plot(demo0719['successRate']*100,'r-',label='successRate',linewidth=2)

横坐标设置时间间隔

import matplotlib.dates as mdate
ax1.xaxis.set_major_formatter(mdate.DateFormatter('%Y-%m-%d %H:%M:%S'))#设置时间标签显示格式
plt.xticks(pd.date_range(demo0719.index[0],demo0719.index[-1],freq='1min'))

纵坐标设置显示百分比

import matplotlib.ticker as mtick
fmt='%.2f%%'
yticks = mtick.FormatStrFormatter(fmt)
ax2.yaxis.set_major_formatter(yticks)

知识点

在matplotlib中，整个图像为一个Figure对象。在Figure对象中可以包含一个，或者多个Axes对象。每个Axes对象都是一个拥有自己坐标系统的绘图区域。其逻辑关系如下：

一个Figure对应一张图片。

Title为标题。Axis为坐标轴，Label为坐标轴标注。Tick为刻度线，Tick Label为刻度注释。¹

Title为标题。Axis为坐标轴，Label为坐标轴标注。Tick为刻度线，Tick Label为刻度注释。

add_subplot()

• 官网matplotlib.pyplot.figure
  pyplot.figure()是返回一个Figure对象的，也就是一张图片。

• add_subplot(args, *kwargs)

The Axes instance will be returned.

twinx()

• matplotlib.axes.Axes method²

ax = twinx()

create a twin of Axes for generating a plot with a sharex x-axis but independent y axis. The y-axis of self will have ticks on left and the returned axes will have ticks on the right.
意思就是，创建了一个独立的Y轴，共享了X轴。双坐标轴！

类似的还有twiny()

ax1.xaxis.set_major_formatter

• set_major_formatter(formatter)

Set the formatter of the major ticker
ACCEPTS: A Formatter instance

DateFormatter()

• class matplotlib.dates.DateFormatter(fmt, tz=None)
  这是一个类，创建一个时间格式的实例。

strftime方法（传入格式化字符串）。

strftime(dt, fmt=None)
Refer to documentation for datetime.strftime.
fmt is a strftime() format string.

FormatStrFormatter()

• class matplotlib.ticker.FormatStrFormatter(fmt)

Use a new-style format string (as used by str.format()) to format the tick. The field formatting must be labeled x
定义字符串格式。

plt.xticks

• matplotlib.pyplot.xticks(args, *kwargs)

# return locs, labels where locs is an array of tick locations and
# labels is an array of tick labels.
locs, labels = xticks()# set the locations of the xticks
xticks( arange(6) )# set the locations and labels of the xticks
xticks( arange(5), ('Tom', 'Dick', 'Harry', 'Sally', 'Sue') )

代码汇总

#coding:utf-8
import matplotlib.pyplot as plt 
import matplotlib as mpl
import matplotlib.dates as mdate
import matplotlib.ticker as mtick
import numpy as np
import pandas as pd
import osmpl.rcParams['font.sans-serif']=['SimHei'] #用来正常显示中文标签
mpl.rcParams['axes.unicode_minus']=False #用来正常显示负号
mpl.rc('xtick', labelsize=20) #设置坐标轴刻度显示大小
mpl.rc('ytick', labelsize=20) 
font_size=30
#matplotlib.rcParams.update({'font.size': 60})%matplotlib inline
plt.style.use('ggplot')data=pd.read_csv('simsendLogConvert_20160803094801.csv',index_col=0,encoding='gb2312',parse_dates=True)columns_len=len(data.columns)
data_columns=data.columnsfor x in range(0,columns_len,2):print('第{}列'.format(x))total=data.ix[:,x]print('第{}列'.format(x+1))successRate=(data.ix[:,x+1]/data.ix[:,x]).fillna(0)yLeftLabel=data_columns[x]yRightLable=data_columns[x+1]print('------------------开始绘制类型{}曲线图------------------'.format(data_columns[x]))fig=plt.figure(figsize=(25,20))ax1=fig.add_subplot(111)#绘制Total曲线图ax1.plot(total,color='#4A7EBB',label=yLeftLabel,linewidth=4)# 设置X轴的坐标刻度线显示间隔ax1.xaxis.set_major_formatter(mdate.DateFormatter('%Y-%m-%d %H:%M:%S'))#设置时间标签显示格式plt.xticks(pd.date_range(data.index[0],data.index[-1],freq='1min'))#时间间隔plt.xticks(rotation=90)#设置双坐标轴，右侧Y轴ax2=ax1.twinx()#设置右侧Y轴显示百分数fmt='%.2f%%'yticks = mtick.FormatStrFormatter(fmt)# 绘制成功率图像ax2.set_ylim(0,110)ax2.plot(successRate*100,color='#BE4B48',label=yRightLable,linewidth=4)ax2.yaxis.set_major_formatter(yticks)ax1.set_xlabel('Time',fontsize=font_size) ax1.set_ylabel(yLeftLabel,fontsize=font_size)ax2.set_ylabel(yRightLable,fontsize=font_size)legend1=ax1.legend(loc=(.02,.94),fontsize=16,shadow=True)legend2=ax2.legend(loc=(.02,.9),fontsize=16,shadow=True)legend1.get_frame().set_facecolor('#FFFFFF')legend2.get_frame().set_facecolor('#FFFFFF')plt.title(yLeftLabel+'&'+yRightLable,fontsize=font_size)plt.savefig('D:\\JGT\\Work-YL\\01布置的任务\\04绘制曲线图和报告文件\\0803\\出图\\{}-{}'.format(yLeftLabel.replace(r'/',' '),yRightLable.replace(r'/',' ')),dpi=300)

参考

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1. Vami-绘图: matplotlib核心剖析 ↩
2. Secondary axis with twinx(): how to add to legend? ↩