Matplotlib 图例未显示在子图上

Question

我无法让图例显示在子图上，这些图例显示得很好并采用我应用的其他格式。我缺少什么？

如果我单独为数据框绘制图表，它会显示图例。如果我为子图添加标签，它会将该标签分配给所有三行。

这是图像。情节与次要情节

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.ticker as ticker
from functools import reduce

%matplotlib notebook

#Source for files
# Per Capita Personal Income
# Ann Arbor https://fred.stlouisfed.org/series/ANNA426PCPI
# MI https://fred.stlouisfed.org/series/MIPCPI
# USA https://fred.stlouisfed.org/series/A792RC0A052NBEA

dfAnnArbor_PCPI = pd.read_csv('PerCapitaPersonalIncomeAnnArborMI.csv', skiprows=1, names=['Date', 'PCPI'])
dfMI_PCPI = pd.read_csv('PerCapitaPersonalIncomeMI.csv', skiprows=1, names=['Date', 'PCPI'])
dfUSA_PCPI = pd.read_csv('PerCapitaPersonalIncomeUSA.csv', skiprows=1, names=['Date', 'PCPI'])

# consolidate three df into one using Date
dfAll = [dfAnnArbor_PCPI, dfMI_PCPI, dfUSA_PCPI]
dfPCPI = reduce(lambda left, right: pd.merge(left, right, on='Date', how='outer'), dfAll)

dfPCPI = dfPCPI.dropna() # drop rows with NaN
dfPCPI.columns = ['Date', 'AnnArbor', 'MI', 'USA'] # rename columns
dfPCPI['Date'] = dfPCPI['Date'].str[:4] # select only year
dfPCPI = dfPCPI.set_index('Date')

dfPCPI_Rel = dfPCPI.apply(lambda x: x / x[0])

dfPCPI_Small = dfPCPI.iloc[8:].copy()
dfPCPI_SmRel = dfPCPI_Small.apply(lambda x: x / x[0])

dfPCPI_SmRel.plot()

fig, ax = plt.subplots(1, 2)

ax0 = ax[0].plot(dfPCPI_Rel, '-', label='a')
ax1 = ax[1].plot(dfPCPI_SmRel, '-', label='test1')

ax[0].legend()

for x in fig.axes:
    for label in x.get_xticklabels():
        label.set_rotation(45)

ax[1].xaxis.set_major_locator(ticker.MultipleLocator(2))

plt.show()

Answer 1

pyplot 中的图例指的是轴实例。因此，如果您希望多个图都有自己的图例，则需要为每个轴调用 legend() 。在你的情况下

ax[0].legend()
ax[1].legend()

此外，当您调用plot()时，您可能希望在每个plot()调用中使用关键字label，以便为每个图例条目添加一个标签。