On Tue, 27 Jan 2004, Sundar Dorai-Raj wrote: > 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.
I think you need a quadtree of the larger set of points, the do lookup for buckets of the smaller one. There is a good deal of information on http://www.cs.umd.edu/~brabec/quadtree/ This isn't an answer within R, the functionality in the gstat contributed package doesn't seem to be at the user level, but it does point to the same site at UMD. Roger > > Thanks, > Sundar > > ______________________________________________ > [EMAIL PROTECTED] mailing list > https://www.stat.math.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > -- Roger Bivand Econonic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Breiviksveien 40, N-5045 Bergen, Norway, voice: +47-55959355, fax: +47-55959393; [EMAIL PROTECTED] ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html