[R-sig-Geo] nearest distance in matrix

[Marius Gilbert]

Dear Barry,

>   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!

I knew there should be way to do it without estimating the full distance 
redistribution matrix O((nrow(mat)*ncol(mat))^2) because the equivalent  
AV Spatial analyst can do rather big raster (3000 x 3000 pixels) in a few 
seconds.

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

It is super quick indeed, I tested it on a 1600 x 250 matrix, ang got the 
output 1600x250 distance matrix in less than 5 seconds on a PIV 1700 Mhz, 
so fairly efficient indeed,

Many thanks, there's no I could have found this myself,

Cheers,

Marius