[R] distance between two matrices
Sundar Dorai-Raj
sundar.dorai-raj at pdf.com
Wed Jan 28 13:38:38 CET 2004
Thanks to Prof. Ripley, Jens, Roger, and Sean. knn1 is exactly what I'm
looking for.
Thanks again,
Sundar
Prof Brian Ripley wrote:
> Sounds like knn classification. See function knn1 in package class.
>
>
>>knn(A, B, 1:nrow(A))
>
>
> gives the same answers as your loop code, and is just a carefully tuned C
> equivalent.
>
> There are faster ways to do this by preprocessing set A discussed e.g. in
> my PRNN book but your numbers took only 11s on my PC.
>
> 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.
>>
>>Thanks,
>>Sundar
>>
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>>
>
>
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