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]])) } } ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.