Hello,
I don't know if it's the fastest but it's more natural to have an index
matrix with two columns only,
one for each coordinate. And it's fast.
fun <- function(valdata, inxdata){
nr <- nrow(inxdata)
nc <- ncol(inxdata)
mat <- matrix(NA, nrow=nr*nc, ncol=2)
i1 <- 1
i2 <- nr
for(j in 1:nc){
mat[i1:i2, 1] <- inxdata[, j]
mat[i1:i2, 2] <- rep(j, nr)
i1 <- i1 + nr
i2 <- i2 + nr
}
matrix(valdata[mat], ncol=nc)
}
fun(vals, indx)
Rui Barradas
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