[R] counts for grouped data
Thomas Lumley
tlumley at u.washington.edu
Thu Sep 4 19:47:09 CEST 2003
On Thu, 4 Sep 2003, Paul Green wrote:
> How does one get counts for grouped data
> from ungrouped data. For example, how can
> I get
>
> X1 X2 Count
> 1 1 1
> 1 2 2
> 2 1 1
> 2 2 1
>
> from
>
> X1 X2
> A A
> A B
> B B
> A B
> B A
>
One possibility is
> df
X1 X2
1 A A
2 A B
3 B B
4 A B
5 B A
> aggregate(rep(1,nrow(df)), df, NROW)
X1 X2 x
1 A A 1
2 B A 1
3 A B 2
4 B B 1
-thomas
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