如何获得两个折线图（使用单独的y轴）以共享相同的日期x轴？

Question

I have two line charts (GMCR stock price, and the S&P 500) over the same period of time. Since the S&P 500 closed yesterday at 1,987 and GMCR closed at 54.65, I have the prices on separate y-axis. My question is how do I get the two lines to share the same date x-axis?

import pandas as pd
from pandas import DataFrame
from matplotlib import pyplot as plt
import pandas.io.data as web
import datetime as dt

end = dt.datetime.today()
df = web.DataReader('GMCR', 'yahoo', '2007-01-01', end)
sp = web.DataReader('^GSPC', 'yahoo', '2007-01-01', end)

fig, ax1 = plt.subplots()
ax2 = ax1.twinx()
ax1.plot(df['Close'],'g-')
ax2.plot(sp['Close'],'b-')

plt.show()

Answer 1

You can add a secondary axis by specifying 'secondary_y=True' when you apply your plot function directly on your dataframe. Also you can force the graphs to be on the same axes by specifying the axis when calling the plot function (in your code above you have two axes ax1 and ax2 instead of a unique one).

import pandas as pd
from pandas import DataFrame
from matplotlib import pyplot as plt
import pandas.io.data as web
import datetime as dt

end = dt.datetime.today()
df = web.DataReader('GMCR', 'yahoo', '2007-01-01', end)
sp = web.DataReader('^GSPC', 'yahoo', '2007-01-01', end)

fig, ax1 = plt.subplots()
df['Close'].plot(ax=ax1,color='g')
sp['Close'].plot(secondary_y=True, ax=ax1,color='b')

plt.show()

Answer 2

Pass the ax to the secondary plot function and set secondary_y to True .

ax = df['Close'].plot(); sp['Close'].plot(ax=ax, secondary_y=True)