Luc, Eik, Jorge,

thanks to all of you!
Nice to see how many different solutions there are for the same  
problem. :)

Best
Henning



Am 07.04.2009 um 22:25 schrieb Jorge Ivan Velez:

>
> Dear Hans,
>
> Try also:
>
> x <- structure(c(2, 1, 2, 1, 3, 2, 4, 1, 4, 3, 4, 3, 5, 2, 5, 1, 6,  
> 1), .Dim = c(2L, 9L))
> tapply(x[2,],x[1,],sum)
> #2 3 4 5 6
> #2 2 7 3 1
>
> HTH,
>
> Jorge
>
>
> On Tue, Apr 7, 2009 at 11:06 AM, Hans-Henning Gabriel <hanshenning.gabriel@gmail.com 
> > wrote:
> Hi,
>
> my problem is as follows:
>
> I have a matrix of two rows like this:
>
> 2 2 3 4 4 4 5 5 6
> 1 1 2 1 3 3 2 1 1
>
> Can I apply something like "group by" in sql? What I want to achieve  
> is the some of second row for each unique entry of first row:
>
> 2 -> 2 (=1+1)
> 3 -> 2
> 4 -> 7 (=1+3+3)
> 5 -> 3 (=2+1)
> 6 -> 1
>
> Thanks!!
> Henning
>
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