[R] distance between two matrices
Liaw, Andy
andy_liaw at merck.com
Wed Jan 28 14:10:41 CET 2004
You can try and see if knn1() in the `class' package (part of the VR bundle)
can handle the job in one shot. If not, just do it in chunks of B. For
your example:
> id <- 1:nrow(A)
> knn1(A, B, id)
[1] 3 2 3
Levels: 1 2 3 4 5 6
(I believe it returns factor, but that can easily be converted back to
numeric.)
HTH,
Andy
> From: Sundar Dorai-Raj
>
> Hi all,
> Say I have a matrix A with dimension m x 2 and matrix B with
> dimension n x 2. I would like to find the row in A that is closest to
> the each row in B. Here's an example (using a loop):
>
> set.seed(1)
> A <- matrix(runif(12), 6, 2) # 6 x 2
> B <- matrix(runif(6), 3, 2) # 3 x 2
> m <- vector("numeric", nrow(B))
> for(j in 1:nrow(B)) {
> d <- (A[, 1] - B[j, 1])^2 + (A[, 2] - B[j, 2])^2
> m[j] <- which.min(d)
> }
>
> All I need is m[]. I would like to accomplish this without using the
> loop if possible, since for my real data n > 140K and m > 1K. I hope
> this makes sense.
>
> Thanks,
> Sundar
>
>
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