python - 创建一个新字段，重复项设为 1，非重复项设为 0

Question

我有这个数据框:

df = pd.DataFrame({'a' : ('road','road','road','highway','house','house'), 
                                   'b' : ('11','23','15','32','17','21')})

给出:

df

       a    b
0   road    11
1   road    23
2   road    15
3   highway 32
4   house   17
5   house   21

我想创建一个新字段，如果根据 a 是重复的，则新文件将采用 1，否则将采用 0。

这里我过滤掉重复的值:

mask = df['a'].duplicated(keep = False)
df[mask]

给出:

       a    b
0   road    11
1   road    23
2   road    15
4   house   17
5   house   21

想要的结果:

       a    b    c
0   road    11   1
1   road    23   1
2   road    15   1
3   highway 32   0
4   house   17   1
5   house   21   1

Answer 1

您可以将 df['a'].duplicated(keep = False) 的结果分配给新列，例如:

<b>df['c']</b> = df['a'].duplicated(keep = False)

结果我们得到:

>>> df
         a   b      c
0     road  11   True
1     road  23   True
2     road  15   True
3  highway  32  False
4    house  17   True
5    house  21   True 

或者如果你想要整数:

df['c'] = df['a'].duplicated(keep = False)<b>.astype(int)</b>

产生预期的结果:

>>> df
         a   b  c
0     road  11  1
1     road  23  1
2     road  15  1
3  highway  32  0
4    house  17  1
5    house  21  1