Python – selecting a particular row from groupby object in python

group-bypandaspython

id    marks  year 
1     18      2013
1     25      2012
3     16      2014
2     16      2013
1     19      2013
3     25      2013
2     18      2014

suppose now I group the above on id by python command.
grouped = file.groupby(file.id)

I would like to get a new file with only the row in each group with recent year that is highest of all the year in the group.

Please let me know the command, I am trying with apply but it ll only given the boolean expression. I want the entire row with latest year.

Best Solution

I cobbled this together using this: Python : Getting the Row which has the max value in groups using groupby

So basically we can groupby the 'id' column, then call transform on the 'year' column and create a boolean index where the year matches the max year value for each 'id':

In [103]:

df[df.groupby(['id'])['year'].transform(max) == df['year']]
Out[103]:
   id  marks  year
0   1     18  2013
2   3     16  2014
4   1     19  2013
6   2     18  2014

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