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))
make the lines below a function of a vector argument and apply it over the rows of B. ?apply for more info. You'll want to know about apply if you want to avoid loops (which is a good approach).
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.
Thing is, the above approach requires all data to be in main memory. i hope this is not a problem.