[R] Aggregate rows to see the number of occurences

[Petr Pikal]

Hallo

On 7 Jun 2004 at 12:18, Nicolas STRANSKY wrote:

> Hi,
> 
> I have a set of data like the following:
>        [,1]  [,2]
> [1,]   10    2
> [2,]    7    0
> [3,]    1    0
> [4,]    1    0
> [5,]   15    0
> [6,]   17    4
> [7,]    4    0
> [8,]   19    8
> [9,]   10    2
> [10,]  19    5

Maybe it can be done more elegantly but table and match can 
probably do what you want.

> tab
   V2 V3
1  10  2
2   7  0
3   1  0
4   1  0
5  15  0
6  17  4
7   4  0
8  19  8
9  10  2
10 19  5

> counts<-table(tab[,1])
> count.no<-as.numeric(names(counts))
> selection<-match(tab[,1],count.no)

> cbind(tab,no=as.numeric(counts[selection]))
   V2 V3 no
1  10  2  2
2   7  0  1
3   1  0  2
4   1  0  2
5  15  0  1
6  17  4  1
7   4  0  1
8  19  8  2
9  10  2  2
10 19  5  2
>

Is this what you want?

Cheers
Petr

> 
> I'd like to aggregate it in order to obtain the frequency (the number
> of occurences) for each couple of values (e.g.: (10,2) appears twice,
> (7,0) appears once). Something cool would be to have this value in a
> third column... I've been looking at aggregate() but either I couldn't
> get the right parameters, or this is not the right tool to use...
> 
> Thank's for any help !
> 
> -- 
> Nicolas STRANSKY
> Équipe Oncologie Moléculaire
> Institut Curie - UMR 144 - CNRS                 Tel : +33 1 42 34 63
> 40 26, rue d'Ulm - 75248 Paris Cedex 5 - FRANCE    Fax : +33 1 42 34
> 63 49
> 
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Petr Pikal
petr.pikal at precheza.cz