Pandas dataframe - create new column based on simple calcuation

问题

I want to make a calculation based on 4 columns in a dataframe and apply the result to a new column.

The 4 columns I'm interested in are as follows.

    rating_1, time_1, rating_2, time_2 col_x col_y etc
0   1              1         1       1     1     1

If time_1 is greater than time_2 I want rating_1 in the new column, if time_2 is greater I want rating_2 in the column.

What's the simplest way to do this please?

回答1:

you can use numpy.where() method:

In [241]: x
Out[241]:
   rating_1  time_1  rating_2  time_2  col_x  col_y
0        11       1        21       1      1      1
1        12       2        21       1      1      1
2        13       1        21       5      1      1
3        14       5        21       5      1      1

In [242]: x['new'] = np.where(x.time_1 > x.time_2, x.rating_1, x.rating_2)

In [243]: x
Out[243]:
   rating_1  time_1  rating_2  time_2  col_x  col_y  new
0        11       1        21       1      1      1   21
1        12       2        21       1      1      1   12
2        13       1        21       5      1      1   21
3        14       5        21       5      1      1   21

回答2:

def myfunc(row):
   if row.time_1 >= row.time_2:
      return row.rating_1
   else:
      return row.rating_2
df.loc[:, 'calculatedColumn'] = df.apply(myfunc, axis = 1)

来源：https://stackoverflow.com/questions/40222181/pandas-dataframe-create-new-column-based-on-simple-calcuation