nearest distance in matrix

Here's another version that probably can be simplified:

nmatdist <- function (m)
{
    v <- as.vector (m)
    ind <- as.matrix (expand.grid (seq (nrow (m)), seq (ncol (m))))
    d <- as.matrix (dist (ind, upper=TRUE))
    ones <- as.numeric (dimnames(ind[v == 1,])[[1]])
    matrix (sapply (seq(nrow(ind)),
        function (x) min (d[x, ones])), nrow=nrow(m))
}

White.Denis at epamail.epa.gov wrote:

Here's another version that probably can be simplified:

nmatdist <- function (m)
{
    v <- as.vector (m)
    ind <- as.matrix (expand.grid (seq (nrow (m)), seq (ncol (m))))
    d <- as.matrix (dist (ind, upper=TRUE))
    ones <- as.numeric (dimnames(ind[v == 1,])[[1]])
    matrix (sapply (seq(nrow(ind)),
        function (x) min (d[x, ones])), nrow=nrow(m))
}

  Eeek! Have you tried that on a 100x100 matrix? Darn near killed my
machine!

  > mt=matrix(runif(10000)>.1,100,100)
  > nmatdist(mt)

   ... near swap death experience...

  The code used by Adrian Baddeley's spatstat routine uses a very neat

method for working out the distances, which involves sweeping along

and columns or something. He did explain it to me when I was in Perth
but I can't recall it now!

  Anyway, its super-quick and uses next-to-no memory. Here's how long

function that calls the spatstat routine takes:

  > unix.time(nmatdist(mt))

  [1] 0.02 0.01 0.02 0.00 0.00

  it was so quick I thought I'd check I'd not done it on a small

by mistake:

  > dim(mt)

  [1] 100 100

Nope!

Baz

  The code used by Adrian Baddeley's spatstat routine uses a very neat 
method for working out the distances, which involves sweeping along rows 
and columns or something. He did explain it to me when I was in Perth 
but I can't recall it now!

  Anyway, its super-quick and uses next-to-no memory. Here's how long my 
function that calls the spatstat routine takes: