python - 组中最后一项的虚拟变量

Question

给定如下所示的数据框，如何添加一列来指示该记录是该 id 的最后一项。

pd.DataFrame({'ID' :["A"] *5 +[ "B"] *2 + ["C"] * 4,
                    'Year': [2017] * 4 +[2018] + [2017, 2019] + [2019] *2 +[2020] * 2,
                    'Quarter': [1,2,3,4,1,3,2,3,4,1,2]})


    ID  Year    Quarter
0   A   2017    1
1   A   2017    2
2   A   2017    3
3   A   2017    4
4   A   2018    1
5   B   2017    3
6   B   2019    2
7   C   2019    3
8   C   2019    4
9   C   2020    1
10  C   2020    2

期望:

    ID  Year    Quarter Last
0   A   2017    1       0
1   A   2017    2       0
2   A   2017    3       0
3   A   2017    4       0
4   A   2018    1       1
5   B   2017    3       0
6   B   2019    2       1
7   C   2019    3       0
8   C   2019    4       0
9   C   2020    1       0
10  C   2020    2       1

Answer 1

您可以使用 keep='last 执行 series.duplicated 并从 1 中减去它

df['Last'] = 1-df['ID'].duplicated(keep='last')
#df['Last'] = 1-df['ID'].duplicated(keep='last').astype(int)

---

   ID  Year  Quarter  Last
0   A  2017        1     0
1   A  2017        2     0
2   A  2017        3     0
3   A  2017        4     0
4   A  2018        1     1
5   B  2017        3     0
6   B  2019        2     1
7   C  2019        3     0
8   C  2019        4     0
9   C  2020        1     0
10  C  2020        2     1