distance between two matrices
Sundar, I'm not sure how much faster (or slower) this might be (perhaps Professor Ripley will help on this one), but one can "trick" a function from the class package called knn1 into doing this for you, I think. From your example:
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) + }
m
[1] 3 2 3 Now using knn1: > knn1(A,B,seq(1,nrow(A),1)) [1] 3 2 3 Levels: 1 2 3 4 5 6 Sean ----- Original Message ----- From: "Sundar Dorai-Raj" <sundar.dorai-raj at pdf.com> To: "R-help" <r-help at stat.math.ethz.ch> Sent: Tuesday, January 27, 2004 3:00 PM Subject: [R] distance between two matrices
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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