python - Pandas 数据帧 : Creating a new column based on data from other columns

Question

我有一个 pandas 数据框，df:

   foo         bar
0  Supplies   Sample X
1  xyz        A   
2  xyz        B
3  Supplies   Sample Y
4  xyz        C
5  Supplies   Sample Z
6  xyz        D
7  xyz        E
8  xyz        F

我想创建一个如下所示的新 df:

   bar
0  Sample X - A
1  Sample X - B
2  Sample Y - C
3  Sample Z - D
4  Sample Z - E
5  Sample Z - F

我是 Pandas 新手，所以我不知道如何实现这一目标。有人可以帮忙吗？

我试过DataFrame.iterrows 但运气不佳。

Answer 1

您可以使用boolean indexing和 ffill :

m = df['foo'].ne('Supplies')

out = (df['bar'].mask(m).ffill()[m]
       .add(' - '+df.loc[m, 'bar'])
       .to_frame().reset_index(drop=True)
       )

输出:

            bar
0  Sample X - A
1  Sample X - B
2  Sample Y - C
3  Sample Z - D
4  Sample Z - E
5  Sample Z - F