[R] regularly lattice & neighbors

[Ben Bolker]

  This seems to work -- there's probably a faster way to do it ...

N <- 3
x <- matrix(1:(N^2),nrow=N,ncol=N)
rowdiff <- function(y,z,mat)abs(row(mat)[y]-row(mat)[z])
coldiff <- function(y,z,mat)abs(col(mat)[y]-col(mat)[z])

rook.case <- function(y,z,mat){coldiff(y,z,mat)+rowdiff(y,z,mat)==1}
bishop.case <- function(y,z,mat){coldiff(y,z,mat)==1 & rowdiff(y,z,mat)==1}
queen.case <- function(y,z,mat){rook.case(y,z,mat) | bishop.case(y,z,mat)}

matrix(as.numeric(sapply(x,function(y)sapply(x,rook.case,y,mat=x))),ncol=N^2,nrow=N^2)
matrix(as.numeric(sapply(x,function(y)sapply(x,bishop.case,y,mat=x))),ncol=N^2,nrow=N^2)
matrix(as.numeric(sapply(x,function(y)sapply(x,queen.case,y,mat=x))),ncol=N^2,nrow=N^2)

On Wed, 29 Mar 2000, Alvaro A. Novo wrote:

> Dear R-users,
> 
> Is there a procedure to identify neighbors in a regular lattice using either a
> "rook" or a "queen" criterium? To be more specific, suppose:
> 
> My lattice:
> 
> 1	2	3
> 4	5	6
> 7	8	9
> 
> "Rook" Neighbors
> 
> 1 has neighbors 2,4
> 2 has neighbors 1,3,5
> ...
> 5 has neighbors 2,4,6,8
> 
> "Queen Neighbors"
> 
> 1 has neighbors 2,4,5
> 2 has neighbors 1,3,4,5,6
> 
> For each case, the final output would be a 9x9 matrix with 0's and 1's.
> 
> I have access to a software that does this for me, but it would be nice to
> avoid importing such matrices.
> 
> Thank you for your help,
> 
> Alvaro Novo
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-- 
Ben Bolker                                  bolker at zoo.ufl.edu
Zoology Department, University of Florida   http://www.zoo.ufl.edu/bolker
318 Carr Hall/Box 118525                    tel: (352) 392-5697
Gainesville, FL 32611-8525                  fax: (352) 392-3704

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