python – 具有MultiIndex的Pandas DataFrame：按DateTime级别值的年份分组

我有和pandas数据帧的multiindex看起来像这样：

# -*- coding: utf-8 -*-
import numpy as np
import pandas as pd

# multi-indexed dataframe
df = pd.DataFrame(np.random.randn(8760 * 3,3))
df['concept'] = "some_value"
df['datetime'] = pd.date_range(start='2016',periods=len(df),freq='60Min')
df.set_index(['concept','datetime'],inplace=True)
df.sort_index(inplace=True)

控制台输出：

df.head()
Out[23]: 
                 0         1         2
datetime                              
2016      0.458802  0.413004  0.091056
2016     -0.051840 -1.780310 -0.304122
2016     -1.119973  0.954591  0.279049
2016     -0.691850 -0.489335  0.554272
2016     -1.278834 -1.292012 -0.637931

df.head()
    ...: df.tail()

Out[24]: 
                 0         1         2
datetime                              
2018     -1.872155  0.434520 -0.526520
2018      0.345213  0.989475 -0.892028
2018     -0.162491  0.908121 -0.993499
2018     -1.094727  0.307312  0.515041
2018     -0.880608 -1.065203 -1.438645

现在我想在’datetime’级别创建年度总和.

我的第一次尝试是以下,但这不起作用：

# sum along years
years = df.index.get_level_values('datetime').year.tolist()
df.index.set_levels([years],level=['datetime'],inplace=True)
df = df.groupby(level=['datetime']).sum()

这对我来说似乎也很沉重,因为这个任务可能很容易实现.

所以这是我的问题：如何获得“日期时间”级别的年度总和？有没有一种简单的方法来通过将函数应用于DateTime级别值来实现这一点？

解决方法

您可以通过第二级multiindex和 year获得 groupby：

# -*- coding: utf-8 -*-
import numpy as np
import pandas as pd

# multi-indexed dataframe
df = pd.DataFrame(np.random.randn(8760  * 3,inplace=True)
df.sort_index(inplace=True)
print df.head() 
                                       0         1         2
concept    datetime                                         
some_value 2016-01-01 00:00:00  1.973437  0.101535 -0.693360
           2016-01-01 01:00:00  1.221657 -1.983806 -0.075609
           2016-01-01 02:00:00 -0.208122 -2.203801  1.254084
           2016-01-01 03:00:00  0.694332 -0.235864  0.538468
           2016-01-01 04:00:00 -0.928815 -1.417445  1.534218

# sum along years
#years = df.index.get_level_values('datetime').year.tolist()
#df.index.set_levels([years],inplace=True)

print df.index.levels[1].year
[2016 2016 2016 ...,2018 2018 2018]
df = df.groupby(df.index.levels[1].year).sum()
print df.head()
               0           1          2
2016  -93.901914  -32.205514 -22.460965
2017  205.681817   67.701669 -33.960801
2018   67.438355  150.954614 -21.381809

或者您可以使用get_level_values和year：

df = df.groupby(df.index.get_level_values('datetime').year).sum()
print df.head()
               0           1          2
2016  -93.901914  -32.205514 -22.460965
2017  205.681817   67.701669 -33.960801
2018   67.438355  150.954614 -21.381809