How to conditionally update DataFrame column in Pandas

Question

With this DataFrame, how can I conditionally set rating to 0 when line_race is equal to zero?

    line_track  line_race  rating fo         


        

Answer 1

df.loc[df['line_race'] == 0, 'rating'] = 0

Answer 2

I have always used method given in Selected answer, today I faced a need where I need to Update column A, conditionally with derived values. the accepted answer shows "how to update column line_race to 0. Below is an example where you have to derive value to be updated with:

df.loc[df['line_race'].isna(), 'rating'] = ( (df['line_race'] - df['line_race2'])/df['line_race2'] )

Using this you can UPDATE dynamic values ONLY on Rows Matching a Condition.

Answer 3

Use numpy.where to say if ColumnA = x then ColumnB = y else ColumnB = ColumnB:

df['rating'] = np.where(df['line_race']==0, 0, df['rating'])