Python Pandas max value in a group as a new column

Question

I am trying to calculate a new column which contains maximum values for each of several groups. I\'m coming from a Stata background so I know the Stata code would be somethi

Answer 1

Use groupby + transform:

df['max'] = df.groupby('group')['odds'].transform('max')

This is equivalent to the verbose:

maxima = df.groupby('group')['odds'].max()
df['max'] = df['group'].map(maxima)

The transform method aligns the groupby result to the groupby indexer, so no explicit mapping is required.