Create repeated increasing sequence based on values in another column

Question

I have col1 in a pandas df. I want to make col2:

col1    col2
1       1
1       2
1       3
1       4
2       2
2       3
2       4
3       3
3       4
4       4

In other words, for each distinct value in col1 I want col2 to be increasing integers that start with the value in col1 and counts up by one until there are no more rows.

The data is structured in a way so that max(col1) = 2450:

when col1 = 1, there are 2450 rows
when col1 = 2, there are 2449 rows
when col1 = 2450, there is 1 row

yatu · Accepted Answer · 2019-03-22 15:13:28Z

4

You could GroupBy column col1, take the cumcount of the groups and add col1:

df['col2'] = df.groupby('col1').cumcount().add(df.col1)

Output

    col1  col2
0     1     1
1     1     2
2     1     3
3     1     4
4     2     2
5     2     3
6     2     4
7     3     3
8     3     4
9     4     4

answered Mar 22, 2019 at 15:13

yatu

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1 Comment

NLR Over a year ago

Nailed it. Thank you!

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