On Jun 28, 2011, at 9:18 PM, Daisy Englert Duursma wrote:
Hello,
I think this is a simple problem but I am not coming up with a simple
solution. I think it just an indexing problem.
I can easily replace values in a matrix from a dataframe when the
dataframe has row and column numbers. In the example below I use row
and column names and I can not get it to work
#make a matrix where rows and columns are the lat and long for a
bounding box of Australia and all elements have the value of -9990
bb<-matrix(c(rep(-9999,691*886)),nrow=691
,ncol
=886,dimnames=list(seq(-10,-44.50,by=-0.05),seq(112,156.25,by=0.05)))
#dfr with row names and col names and values to be replaced in the
matrix
dfr <- data.frame(cbind(x=seq(120,125,by=0.05), y=-25, var.1=1))
#insert the values from the dfr into the matrix
bb[dfr$x,dfr$y]<-d$var.1
Indexing with a two column matrix is possible, but those vectors are
not legitimate indices even if you bundle them into a two column
matrix. (dfr$y's are all -25, so at least the error report is
informative).
These will return indices:
sapply(as.character(dfr$y), function(x) which(x== dimnames(bb)[[1]]))
sapply(as.character(dfr$x), function(x) which(x== dimnames(bb)[[2]]))
So try:
> #insert the values from the dfr into the matrix
> bb[matrix(c(sapply(as.character(dfr$y), function(x) which(x==
dimnames(bb)[[1]])), sapply(as.character(dfr$x), function(x)
which(x== dimnames(bb)[[2]]))), ncol=2)] <- dfr[["var.1"]]
Thanks for your help,
Daisy
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David Winsemius, MD
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