Pandas：为具有多列的数据框实现 groupby + 聚合的优雅方法？

Question

我有一个数据框my_df，然后我想创建一个新的数据框new_df。每个new_df 列都是由groupby my_id 创建的，然后在my_df 中取一列的max。

下面是我的代码，它工作正常。但是，我想知道有没有更好的方法？特别是在未来我将处理数百列而不是仅仅 6 列？非常感谢！

tmp_df1 = my_df.groupby(['my_id'], as_index=False).col_A.agg({"max_A": "max"})   
tmp_df2 = my_df.groupby(['my_id'], as_index=False).col_B.agg({"max_B": "max"})
tmp_df3 = my_df.groupby(['my_id'], as_index=False).col_C.agg({"max_C": "max"}) 
tmp_df4 = my_df.groupby(['my_id'], as_index=False).col_D.agg({"max_D": "max"})
tmp_df5 = my_df.groupby(['my_id'], as_index=False).col_E.agg({"max_E": "max"})
tmp_df6 = my_df.groupby(['my_id'], as_index=False).col_F.agg({"max_F": "max"})

combine_df1 = pd.merge(tmp_df1,tmp_df2,how="inner",on=['my_id'])
combine_df2 = pd.merge(combine_df1,tmp_df3,how="inner",on=['my_id'])
combine_df3 = pd.merge(combine_df2,tmp_df4,how="inner",on=['my_id'])
combine_df4 = pd.merge(combine_df3,tmp_df5,how="inner",on=['my_id'])
new_df = pd.merge(combine_df4,tmp_df6,how="inner",on=['my_id'])

Answer 1

考虑示例数据框my_df

np.random.seed([3,1415])

my_df = pd.DataFrame(dict(
    my_id=list('WXYZ') * 4,
    col_A=np.random.randint(10, size=16),
    col_B=np.random.randint(10, size=16),
    col_C=np.random.randint(10, size=16),
    col_D=np.random.randint(10, size=16),
    col_E=np.random.randint(10, size=16),
    col_F=np.random.randint(10, size=16),
))

my_df

    col_A  col_B  col_C  col_D  col_E  col_F my_id
0       0      3      6      1      9      3     W
1       2      2      4      5      8      5     X
2       7      4      7      2      0      8     Y
3       3      3      6      8      4      5     Z
4       8      3      2      2      3      1     W
5       7      6      6      4      0      5     X
6       0      7      6      7      4      1     Y
7       6      7      5      6      1      4     Z
8       8      4      2      9      5      3     W
9       6      5      8      4      8      9     X
10      0      3      7      2      6      5     Y
11      2      7      5      4      0      5     Z
12      0      5      8      6      8      7     W
13      4      9      4      3      7      0     X
14      9      8      7      8      4      3     Y
15      7      7      6      3      6      2     Z

您只想使用groupby 和max

new_df = my_df.groupby('my_id', as_index=False).max()
new_df

  my_id  col_A  col_B  col_C  col_D  col_E  col_F
0     W      8      5      8      9      9      7
1     X      7      9      8      5      8      9
2     Y      9      8      7      8      6      8
3     Z      7      7      6      8      6      5

如果要更改列的名称：

my_df.groupby('my_id').max() \
    .rename(columns=lambda x: x.replace('col_', '')) \
    .add_suffix('_max').reset_index()

  my_id  A_max  B_max  C_max  D_max  E_max  F_max
0     W      8      5      8      9      9      7
1     X      7      9      8      5      8      9
2     Y      9      8      7      8      6      8
3     Z      7      7      6      8      6      5

或者

my_df.groupby('my_id').max() \
    .rename(columns=lambda x: x.rsplit('_', 1)[1] + '_max').reset_index()

  my_id  A_max  B_max  C_max  D_max  E_max  F_max
0     W      8      5      8      9      9      7
1     X      7      9      8      5      8      9
2     Y      9      8      7      8      6      8
3     Z      7      7      6      8      6      5