Python：具有不断增长的列的数据透视表

Question

我有一张桌子 df:

    class teacher January February
0     A    Mary       4        3
1     B     Ann       5        7
2     C   Kevin       6        8

代码：

import pandas as pd
df = pd.DataFrame( {'class':['A', 'B', 'C'], 
                    'teacher':['Mary', 'Ann', 'Kevin'],
                    'January':['4', '5', '6'], 
                    'February':['3', '7', '8']
                   } )

我需要将月份列转为行作为 new_df:

     month     class teacher count
0   January      A    Mary      4     
1   January      B    Ann       5        
2   January      C    Kevin     6        
3   February     A    Mary      3     
4   February     B    Ann       7        
5   February     C    Kevin     8       

月份列将来可能会像这样增长，所以我需要将整个月份转为 new_df:

未来的df：

    class teacher January February March
0     A    Mary       4        3    4
1     B     Ann       5        7    6
2     C   Kevin       6        8    4

不太确定如何通过数据透视将 df 转换为 new_df 。我需要先交换列和行吗？

Answer 1

这是一种方法：

(
    df.set_index(['class', 'teacher'])
      .stack()
      .rename_axis(['class', 'teacher', 'month'])
      .rename('count')
      .reset_index()
)

  class teacher     month count
0     A    Mary   January     4
1     A    Mary  February     3
2     B     Ann   January     5
3     B     Ann  February     7
4     C   Kevin   January     6
5     C   Kevin  February     8