[R] group by in data.frame

[zem]

Yeah, you are right
i want to post an short example what i want to do .. and in the meantime i
solved the problem ... 
but here is: 
i have something like this dataframe: 
c1<-c(1,2,3,2,2,3,1,2,2,2)
c2<-c(5,6,7,7,5,7,5,7,6,6)
c3<-rnorm(10)
x<-cbind(c1,c2,c3)
> x
      c1 c2          c3
 [1,]  1  5  0.08279036
 [2,]  2  6  0.59135988
 [3,]  3  7  1.45520468
 [4,]  2  7 -1.70094640
 [5,]  2  5  0.13065228
 [6,]  3  7 -1.12080980
 [7,]  1  5  0.42779354
 [8,]  2  7 -1.53111972
 [9,]  2  6  0.29299987
[10,]  2  6 -0.01602095

#whith aggregate i receive this:
>aggregate(x[,3],list(x[,1],x[,2]),mean)
  Group.1 Group.2          x
1       1       5  0.2552920
2       2       5  0.1306523
3       2       6  0.2894463
4       2       7 -1.6160331
5       3       7  0.1671974


and the problem was that i was grouping by 2 columns, so i couldn't copy the
result to x.

the solution was i made another column with paste(x[,1],x[,2],sep="_")
and then i used the solution from this link:
http://tolstoy.newcastle.edu.au/R/help/06/07/30184.html
so i solved my problem

Ivan, many thanks for your support and quik responses! :) 

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