If you want count:
xtabs( ~ x + y, X)
or sum:
xtabs(z ~ x + y, X)
On Tue, Jan 25, 2011 at 5:25 PM, Ryan Utz wrote:
> Hi R-users,
>
> I'm trying to find an elegant way to count the number of rows in a
> dataframe
> with a unique combination of 2 values in the dataframe. My data is
> specifically one column with a year, one with a month, and one with a day.
> I'm trying to count the number of days in each year/month combination. But
> for simplicity's sake, the following dataset will do:
>
> x<-c(1,1,1,1,2,2,2,2,3,3,3,3)
> y<-c(1,1,2,2,3,3,4,4,5,5,6,6)
> z<-c(1,2,3,4,5,6,7,8,9,10,11,12)
> X<-data.frame(x y z)
>
> So with dataset X, how would I count the number of z values (3rd column in
> X) with unique combinations of the first two columns (x and y)? (for
> instance, in the above example, there are 2 instances per unique
> combination
> of the first two columns). I can do this in Matlab and it's easy, but since
> I'm new to R this is royally stumping me.
>
> Thanks,
> Ryan
>
> --
> Ryan Utz
> Postdoctoral research scholar
> University of California, Santa Barbara
> (724) 272 7769
>
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>
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--
Henrique Dallazuanna
Curitiba-Paraná-Brasil
25° 25' 40" S 49° 16' 22" O
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