[R] Spatial: number of independent components?

[Daniel Malter]

Hi all, I am sorry if this is a very basic quesion, but I have no experience
with analyzing spatial data and could not find the right function/package
quickly. Any hints would be much appreciated. I have a matrix of spatial
point patterns like the one below and want to find the number of independent
components (if that's the right term) in that matrix (or in that image).

x=matrix(c(0,1,0,0,0,
          0,1,1,0,0,
          0,0,0,0,0,
          0,0,0,1,0,
          0,0,0,1,0),nrow=5)

image(x)

I can find the number of populated points easily

table(x)  #or more generally
sum(x!=0)

But I want to find the number of independent components. The answer in this
example should be 2. There are three criteria to the function I am seeking:

1. Points that have a neighboring nonzero point should be counted as one
contiguous component. 

2. The function should respect that the matrix is projected on a torso. That
is, points in the leftmost column border points in the rightmost column and
points in the top row border points in the bottom row (if they are
contiguous when you wrap the image around a cylinder).

3. The function should be fast/efficient since I need to run this over
thousands of images/matrices.

Is anyone aware of an implementation of such a function?

Thanks much for your help,
Daniel
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