[R] index values of one matrix to another of a different size

[Rui Barradas]

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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