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MathGroup Archive 2007

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Identifying clusters of adjacent points on a lattice

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81384] Identifying clusters of adjacent points on a lattice
  • From: Gareth Russell <russell at njit.edu>
  • Date: Fri, 21 Sep 2007 03:10:20 -0400 (EDT)

Hi,

Is there any way to use the built-in clustering routines to find
clusters of ajacent elements on a 2d lattice? For example, I might
generate a 'map' with

SeedRandom[1];
testMap = =E2=80=A8 Last[CellularAutomaton[{1018, {2, {{0, 2, 0}, {2, 1, 2},
{0, 2, 0}}}, {1, =E2=80=A8     1}}, Table[If[Random[Real] < 0.1, 1, 0], {100},
{100}], 10]];

I would then like to find and label the separate 'patches' consisting
of clusters of 1's. Ultimately, I'm looking for a list of {x,y,id}
triples where the x and y are the coordinates of each 1 and the id is a
number that identifies the patch to which that element belongs, but the
trick is to find the clusters. I can't see how any of the included
options for FindClusters would perform this particular test (each
cluster must consist of elements connected to at least one other
element by a distance of 1).

Of perhaps there is another way?

Thanks,

Gareth
--
Gareth Russell
NJIT



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