Get next row after groupby

Question

My question is similar to this one : Get next row besides the previous row after groupby but not quite the same. I’d like to get the first row appearing after a group concatenated to each row of the group.

So if I have:

ID     value      counts      date
1      1          3           1/2/2020
1      2          10          10/2/2020
1      3          5           15/2/2020
2      1          6           3/4/2020
2      2          2           10/4/2020

I’d like to have:

ID     value      counts      date         NextID    NextValue     NextCounts    NextDate
1      1          3           1/2/2020     2         1             6             3/4/2020
1      2          10          10/2/2020    2         1             6             3/4/2020
1      3          5           15/2/2020    2         1             6             3/4/2020
2      1          6           3/4/2020     3         4             1             11/12/2020
2      2          2           10/4/2020    3         4             1             11/12/2020
3      4          1           11/12/2020   nan       nan           nan           nan

Asked By: Achille G

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Source

Answer 1

You can use a merge on the groupby.first+shift:

out = df.merge(df.groupby('ID', sort=False).first()
                 .assign(ID=lambda d: d.index).shift(-1)
                 .add_prefix('Next').iloc[:-1],
               left_on='ID', right_index=True, how='left')

Output:

   ID  value  counts        date  Nextvalue  Nextcounts    Nextdate  NextID
0   1      1       3    1/2/2020        1.0         6.0    3/4/2020     2.0
1   1      2      10   10/2/2020        1.0         6.0    3/4/2020     2.0
2   1      3       5   15/2/2020        1.0         6.0    3/4/2020     2.0
3   2      1       6    3/4/2020        4.0         1.0  11/12/2020     3.0
4   2      2       2   10/4/2020        4.0         1.0  11/12/2020     3.0
5   3      4       1  11/12/2020        NaN         NaN         NaN     NaN

Answered By: mozway

Get next row after groupby

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