python - 如何防止聚合函数删除列？

Question

我有一个包含 3 列的数据框。我按一列进行分组，并希望聚合另一列的这些组的最大值。不过我想保留我的第三栏。 This is the dataframe I start with 。然后我按“邻居”分组并聚合“金额”的最大值。

agg_dict = {"Amount": np.max}
listings_group.groupby("neighbourhood").agg(agg_dict).reset_index()

但是this is the dataframe I end up with 。它几乎满足了我的要求，但我还想保留我的列“room_type”。

编辑

分组前的数据框

neighbourhood   room_type   Amount
0   Allerton    Entire home/apt 7
1   Allerton    Private room    14
2   Allerton    Shared room 2
3   Arden Heights   Private room    4
4   Arrochar    Entire home/apt 12
5   Arrochar    Private room    3
6   Arverne Entire home/apt 29
7   Arverne Private room    43
8   Arverne Shared room 2

分组后的数据框

    neighbourhood   Amount
0   Allerton    14
1   Arden Heights   4
2   Arrochar    12
3   Arverne 43
4   Astoria 458
5   Bath Beach  7
6   Battery Park City   45
7   Bay Ridge   55

Answer 1

尝试使用 groupby idxmax 进行切片上Amount

listings_group.loc[listings_group.groupby("neighbourhood")['Amount'].idxmax()]

Out[347]:
   neighbourhood        room_type  Amount
1  Allerton       Private room     14
3  Arden Heights  Private room     4
4  Arrochar       Entire home/apt  12
7  Arverne        Private room     43

<小时/>

逐步:

groupby idxmax在专栏Amount将返回值为 Amount 的行索引每组最多。

m = listings_group.groupby("neighbourhood")['Amount'].idxmax()

Out[348]:
neighbourhood
Allerton         1
Arden Heights    3
Arrochar         4
Arverne          7
Name: Amount, dtype: int64

.loc与 m将切片并仅返回索引值等于 m 中的值的行

listings_group.loc[m]

Out[352]:
   neighbourhood        room_type  Amount
1  Allerton       Private room     14
3  Arden Heights  Private room     4
4  Arrochar       Entire home/apt  12
7  Arverne        Private room     43