try this:
> # create indexing vector to select 3 adjacent columns
> indx <- sapply(seq(1, 36, 3), seq, length = 3)
> # process each row of the table
> ans <- t(apply(data, 1, function(.row){
+ # use indx to sum up the columns
+ apply(indx, 2, function(.indx){
+ sum(.row[.indx])
+ })
+ }))
> ans
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
[1,] 18 63 108 153 198 243 189 36 81 126 171 216
[2,] 21 66 111 156 201 246 192 39 84 129 174 219
[3,] 24 69 114 159 204 249 195 42 87 132 177 222
[4,] 27 72 117 162 207 252 198 45 90 135 180 225
[5,] 30 75 120 165 210 255 102 48 93 138 183 228
On Mon, Dec 20, 2010 at 5:48 AM, Anne-Christine Mupepele
<anne-chr....@web.de> wrote:
> Hi,
> I have the following problem:
>
> I have a data.frame with 36 sample sites (colums) for which I have covariates
> in 3 categories: Area, Month and River. Each Area consists of 3 rivers, which
> were sampled over 3 month. Now I want to fuse River 1-3 for one area in one
> month. To get a data.frame with 12 colums.
> I am trying to do a "for loop" (which may be a complicated solution, but I
> don't see an easier way), which is not working, apparently because a[,ij] or
> a[,c(i,j)] is not working as a definition of the matrix with a double
> condition in the colums.
> How can I make it work or what would be an easier solution?
>
> Thank you for your help,
> Anne
>
> data=data.frame(matrix(1:99,nrow=5,ncol=36))
> colnames(data)=c(paste("plot",1:36))
> cov=data.frame(rep(1:3,12),c(rep("Jan",12),rep("Feb",12),rep("Mar",12)),rep(c(1,1,1,2,2,2,3,3,3,4,4,4),3))
> dimnames(cov)=list(colnames(data),c("River","Month","Area"))
>
> ###loop###
> a=matrix(nrow=dim(data)[1],ncol=length(levels(factor(cov$Month)))*length(levels(factor(cov$Area))))
>
> for(i in 1:length(levels(factor(cov$Month))))
> {
> for(j in 1:length(levels(factor(cov$Area))))
> {
> a[,ij]=as.numeric(rowSums(data[,factor(cov$Month)==levels(factor(cov$Month))[i]&factor(cov$Area)==levels(factor(cov$Area))[j]]))
> }
> }
>
> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
--
Jim Holtman
Data Munger Guru
What is the problem that you are trying to solve?
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