python - 如何根据先前的列有条件地设置空列值

Question

我想插入第 3 列的值，如下所示:

A+ if col 1 is a and col 2 is positive
A- if col 1 is a and col 2 is negative
B+ if col 1 is B and col 2 is positive
B- if col 1 is B and col 2 is negative

数据:

    COL1  COL2  COL3
0     a    -2
1     a     4
2     b     10
3     b     -8
4     a     10
5     b     5

因此我想要一个结果 df:

     COL1  COL2  COL3
0     a    -2      A-
1     a     4      A+
2     b     10     B+
3     b     -8     B-
4     a     10     A+
5     b     5      B+

Answer 1

anky_91 注意到，np.where 几乎是重复的:

df['COL3'] = df.COL1.str.upper() + np.where(df.COL2.gt(0),'+', '-')

给出预期的输出:

  COL1  COL2 COL3
0    a    -2   A-
1    a     4   A+
2    b    10   B+
3    b    -8   B-
4    a    10   A+
5    b     5   B+