[R] Aggregate weights for a unique set of rows

[Weiser, Constantin]

Hi, all together. I have - a maybe trivial - problem with aggregating a
list of weights.

Here is the problem:
 - At first I have set of nodes (X/Y-coordinates) and associated weights,
where the set
   of nodes is typically not unique
 - I want to get a set of unique nodes and the sum of associated weights

I am grateful for any help


See for example:

	# weights:
	w <- c(1, 1, 1, 1, 1)

	# not unique set of nodes (X/Y-coordinates):
	nodes <- matrix(c(1,2,3,4,5,6,1,2,1,4),ncol=2, byrow=T)


desired Result:

	#nodes
	    [,1] [,2]
	[1,]    1    2
	[2,]    3    4
	[3,]    5    6
	[4,]    1    4



	#weights
	2 1 1 1



That is my solution, but it is very slow (typical size of nodes -->
200000x2):

weights <- c(1, 1, 1, 1, 1)
nodes <- matrix(c(1,2,3,4,5,6,1,2,1,4),ncol=2, byrow=T)


## to be replaced by a faster code
	drop.index <- duplicated(nodes)
	n.unique <- nodes[!drop.index, ]
	w.unique <- numeric(length(n.unique[,1]))

	lw <- length(weights)
	for (i in seq_along(w.unique)){
		index <- as.logical(2==rowSums(nodes==matrix(rep(n.unique[i,],lw),byrow
= TRUE, nrow=lw)))
		w.unique[i] <- sum(weights[index])
	}
##

n.unique
w.unique





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|              /eiser, Constantin
|             / Gutenberg University of Mainz, Germany
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