python - 使用 Pandas 在不同轴上绘制条形图和时间序列图

Question

我有一个 pandas 数据框，它是从具有这种结构的 .csv 文件中读取的:

Date,       Latitude,   Longitude,        Brand,        Pump, AKI,  Trip Miles,  Total Miles, Gallons,  MPG,    PPG,    Total,  Tires,  MPG-D,
11/03/2013, 40° 1.729', -105° 15.516',    Boulder Gas,  2,    87,   134.3,       134.3,       6.563,    20.46,  3.319,  21.78,  Stock,  ,
11/17/2013, 40° 1.729', -105° 15.516',    Boulder Gas,  2,    87,   161.8,       296.0,       7.467,    21.67,  3.279,  24.48,  Stock,  ,
11/27/2013, 40° 0.872', -105° 12.775',    Buffalo Gas,  6,    87,   180.8,       477.0,       8.096,    22.33,  3.359,  27.19,  Stock,  ,
12/07/2013, 40° 1.729', -105° 15.516',    Boulder Gas,  6,    87,   265.1,       742.0,       12.073,   21.96,  3.179,  38.38,  Stock,  ,
12/11/2013, 40° 2.170', -105° 15.522',    Circle K,     4,    87,   240.9,       983.0,       9.868,    24.41,  3.179,  31.37,  Stock,  ,
12/15/2013, 40° 8.995', -105° 7.876',     Shell,        3,    87,   188.7,       1172,        8.596,    21.95,  3.059,  26.30,  ,       ,
12/21/2013, 40° 1.770', -105° 15.481',    Conoco,       3,    87,   113.8,       1286,        5.517,    20.62,  3.139,  17.32,  Winter, ,
01/09/2014, 40° 1.729', -105° 15.516',    Boulder Gas,  2,    87,   139.5,       1426,        7.181,    19.42,  3.279,  23.55,  Winter, 21.3,
01/13/2013, 40° 1.770', -105° 15.481',    Conoco,       7,    87,   260.8,       1688,        11.177,   23.33,  3.239,  36.20,  Winter, 25.5,
01/18/2014, 40° 1.729', -105° 15.516',    Boulder Gas,  2,    87,   102.0,       1790,        4.401,    23.18,  3.239,  14.26,  Winter, 25.5,
02/02/2014, 39° 59.132', -105° 14.962',   King Soopers, 5,    87,   175.3,       1965,        8.436,    20.78,  3.019,  25.47,  Winter, 24.0,
02/03/2014, 40° 1.770', -105° 15.481',    Conoco,       3,    87,   249.9,       2215,        10.452,   23.91,  3.219,  33.64,  Winter, 25.2,
02/08/2014, 40° 2.170', -105° 15.522',    Circle K,     7,    87,   186.4,       2402,        8.565,    21.76,  3.239,  27.74,  Winter, 24.3,
02/13/2014, 40° 1.729', -105° 15.516',    Boulder Gas,  8,    87,    79.6,       2481,        4.125,    19.30,  3.439,  14.19,  Winter, 21.3,
03/06/2014, 40.014460, -105.225034,       Conoco,       5,    87,   172.4,       2654,        8.618,    20.00,  3.779,  32.57,  Winter, 21.9,
03/09/2014, 40.029498, -105.258117,       Conoco,       6,    87,   230.4,       2884,        9.016,    25.55,  3.759,  33.89,  Winter, 27.3,
03/17/2014, 40.036236, -105.258763,       Conoco,       6,    87,   130.1,       3014,        5.368,    24.24,  3.719,  19.96,  Winter, 25.8,
03/24/2014, 40.036236, -105.258763,       Conoco,       1,    87,   282.3,       3297,       11.540,    24.46,  3.719,  42.92,  Winter, 27.3,

我想制作一个图表，其中 x 轴是日期，左侧 y 轴是英里/加仑，右侧 y 轴是英里。在此图中，我想以一种颜色显示“MPG”列的时间序列，以另一种颜色显示“MPG-D”的时间序列，并以第三种颜色显示“行程里程”列的条形图。

我一直在努力关注http://pandas.pydata.org/pandas-docs/stable/visualization.html并具有下面的代码，但它会生成一个条形图和两个时间序列图，其中所有内容都在同一轴上并且未显示 y 标签。

%matplotlib inline
import pandas as pd
import matplotlib.pyplot as plt

data = pd.read_csv('mpg.csv', skipinitialspace=True,index_col='Date')
plt.figure()
ax = data['Trip Miles'].plot(kind='bar',secondary_y=['Trip Miles'])
ax.right_ax.set_ylabel('Miles')
ax.set_ylabel('Miles/Gallon')
data['MPG'].plot()
data['MPG-D'].plot()

Answer 1

您需要更明确地指定轴。像这样尝试:

%matplotlib inline
import pandas as pd
import matplotlib.pyplot as plt

fig, tsax = plt.subplots()
barax = tsax.twinx()

data = pd.read_csv('mpg.csv', skipinitialspace=True,index_col='Date')
data['Trip Miles'].plot(kind='bar', ax=barax)
barax.set_ylabel('Miles')
tsax.set_ylabel('Miles/Gallon')
data['MPG'].plot(ax=tsax)
data['MPG-D'].plot(ax=tsax)

编辑

这里的一个大问题是 pandas 条形图和线图以根本不同的方式格式化 x 轴。具体来说，条形图试图为每个条形图制作带有刻度和标签的定性尺度。但在这里您似乎对获得更像典型时间序列的格式感兴趣。

因此，我建议您忘记双轴图表。相反，只需在两个完全独立的轴上绘制。像这样:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.gridspec as mgrid
import pandas as pd

fig = plt.figure(figsize=(12,5))
grid = mgrid.GridSpec(nrows=2, ncols=1, height_ratios=[2, 1])

barax = fig.add_subplot(grid[0])
tsax = fig.add_subplot(grid[1])
data = pd.DataFrame(np.random.randn(10,3), columns=list('ABC'), index=pd.DatetimeIndex(freq='1M', start='2012-01-01', periods=10))

data['A'] **= 2
data['A'].plot(ax=barax, style='o--')
barax.set_ylabel('Miles')
tsax.set_ylabel('Miles/Gallon')

barax.xaxis.tick_top()

data['B'].plot(ax=tsax)
data['C'].plot(ax=tsax)
fig.tight_layout()

这给了我:

但是，如果您真的需要条形图或者您真的想要所有东西都在同一个双 x 轴上，那么您必须像这样使用 matplotlib 的 API 进行绘图:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.gridspec as mgrid
import pandas as pd

fig, tsax = plt.subplots(figsize=(12,5))
barax = tsax.twinx()

data = pd.DataFrame(np.random.randn(10,3), columns=list('ABC'), index=pd.DatetimeIndex(freq='1M', start='2012-01-01', periods=10))
data['A'] **= 2

# the `width` is specified in days -- adjust for your data
barax.bar(data.index, data['A'], width=5, facecolor='indianred')

barax.set_ylabel('Miles')
tsax.set_ylabel('Miles/Gallon')

barax.xaxis.tick_top()

fig.tight_layout()

tsax.plot(data.index, data['B'])
tsax.plot(data.index, data['C'])

然后给了我