Pandas 根据另一列的值更新一列多行的值

Question

I have a dataframe like:

 column1 column2 a 32 b 175 b 165 a 80

and I want to update the value (multiplied by 10) of every row of column2 whose value in column1 == 'a'. The result is expected to be like:

 column1 column2 a 320 b 175 b 165 a 800

Answer 1

Very short with loc :

df.loc[df['column1']=='a', 'column2'] *= 10

You get:

  column1  column2
0       a      320
1       b      175
2       b      165
3       a      800

Answer 2

Try np.where

df['column2'] = np.where(df['column1'].eq('a'), df['column2'].mul(10), df['column2'])

Or df.mask

df['column2'] = df['column2'].mask(df['column1'].eq('a'), df['column2'].mul(10))

  column1  column2
0       a      320
1       b      175
2       b      165
3       a      800