I am trying to create a column (is_max) that has either 1 if a column B is the maximum in a group of values of column A or 0 if it is not.
Example:
[Input]
A B
1 2
2 3
1 4
2 5
[Output]
A B is_max
1 2 0
2 5 0
1 4 1
2 3 0
What I'm trying:
df['is_max'] = 0
df.loc[df.reset_index().groupby('A')['B'].idxmax(),'is_max'] = 1
Fix your code by remove the reset_index
df['is_max'] = 0
df.loc[df.groupby('A')['B'].idxmax(),'is_max'] = 1
df
Out[39]:
A B is_max
0 1 2 0
1 2 3 0
2 1 4 1
3 2 5 1
I make assumption A is your group now that you did not state
df['is_max']=(df['B']==df.groupby('A')['B'].transform('max')).astype(int)
or
df1.groupby('A')['B'].apply(lambda x: x==x.max()).astype(int)