Jojje Andersson:
> I have a dataframe with in one column an id-variable and in another a
> year-variable. One id-number can occur several years. I have sorted the
> dataframe on id then on year so the same id-number is sorted by year with
> the first occurens at top.
>
> Now I want to make a subset of this dataframe with just the first year the
> id-number occur, so the first case of every id.
>
> Id Year
> 123456 2001
> 123456 2002
> 123456 2003
> 655432 2001
> 655432 2002
> 655432 2003
The following should work (even if the data frame was *not* sorted):
Id = c(123456,123456,123456,655432,655432,655432)
Year = c(2001,2002,2003,2001,2002,2003)
d = data.frame(Id, Year)
aggregate(d, list(Id), min)[,-1]
Output:
Id Year
1 123456 2001
2 655432 2001
--
Karl Ove Hufthammer
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