带join的groupby agg无法产生预期的输出 [英] Groupby agg with join not produce the expected output

问题描述

我的数据框如下

   Wash_Month  Wash_Day
0           3         2
1           4         3

预期的产量是

#d={'Wash_Month':'Wash_Month/Wash_Day','Wash_Day':'Wash_Month/Wash_Day'}

#df.T.astype(str).groupby(d).agg(','.join)
Out[329]: 
                       0    1
Wash_Month/Wash_Day  3,2  4,3

如您所见，我首先进行转置T.

As you saw , I first do the transpose T.

如果我们groupby与axis=1并删除了T，我希望得到同样的输出结果.

If we groupby with axis=1 and remove the T, I expected the same out put.

df.astype(str).groupby(d,axis=1).agg(','.join)
Out[330]: 
   Wash_Month/Wash_Day
0  Wash_Month,Wash_Day
1  Wash_Month,Wash_Day

输出与预期输出不匹配.在agg和join以及axis=1的groupby上是否存在特定问题

The out put is mismatched with expected output . Is there specific problem onagg with join with groupby of axis=1

由于sum之类的其他agg功能正常运行

Since other agg function like sum work as normal

df.astype(str).groupby({'Wash_Month':'Wash_Month/Wash_Day','Wash_Day':'Wash_Month/Wash_Day'}, axis=1).sum()
Out[332]: 
   Wash_Month/Wash_Day
0                 32.0 # str 3 + str 2
1                 43.0

关于为什么结果变为浮动而不是str检查的原因链接

About why the result become float rather than a str check link

感谢您的帮助:-)

推荐答案

以下是提示:

def f(x):
    print(x)
    print(type(x))
    return 1

df.astype(str).groupby(d,axis=1).agg(f)

输出:

  Wash_Month Wash_Day
0          3        2
1          4        3
<class 'pandas.core.frame.DataFrame'>

请注意输出是一个数据框.

Note the output is a dataframe.

相对于:

def f(x):
    print(x)
    print(type(x))
    return 1

df.T.astype(str).groupby(d).agg(f)

输出:

Wash_Month    3
Wash_Day      2
Name: 0, dtype: object
<class 'pandas.core.series.Series'>
Wash_Month    4
Wash_Day      3
Name: 1, dtype: object
<class 'pandas.core.series.Series'>

每个系列都调用f，因此"join"将列标题串联起来.

Which f gets called with each series, hence 'join' is concatenating the column headers.

我无法通过解释源代码来解释它，但是看来groupby和astype(str)会导致agg在每种情况下的动作都不同.

I can't explain it with digging through the source code, but it appears that the groupby along with astype(str) is causing agg to act differently in each situation.

这篇关于带join的groupby agg无法产生预期的输出的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！