Construct neighbours for a GridTopology

The function builds a neighbours list for a grid topology. It works for a k-dimentional grid topology, k>=1.

Usage

grid2nb(grid, d = grid@cells.dim,
        queen = TRUE, nb = TRUE, self = FALSE)

Arguments

grid: An object of class GridTopology. One can avoid to supply this by just suplying the dimentions in the d argument.
d: A scalar (for one dimentional grid) or a length k vector specyfying the number of grid cells in each direction of the k dimentions.
queen: Logical. Default is TRUE. To inform if the queen neighbourhood structure should be considered. If FALSE, only a hyper-cube with a common face will be considered neighbour. If TRUE, a single shared coordinate meets the contiguity condition.
nb: Default TRUE. If TRUE, return the result as a neighbours list with class nb. If FALSE, the result is a matrix with 3^k columns if self = TRUE or 3^k-1 if self = FALSE. Zeros are used for hyper-cubes at boundaries.
self: Default FALSE, to indicate if the hyper-cube neighbour itself should be considered a neighbour.

Value

Either a matrix, if “nb” is FALSE or a neighbours list with class nb. See card for details of “nb” objects.

Note

This applies to a k-dimentional grid topology.

Author

Elias T Krainski eliaskrainski@gmail.com

Examples

nb <- grid2nb(d = c(5L, 5L, 5L))
nb
#> Neighbour list object:
#> Number of regions: 125 
#> Number of nonzero links: 2072 
#> Percentage nonzero weights: 13.2608 
#> Average number of links: 16.576 
summary(nb)
#> Neighbour list object:
#> Number of regions: 125 
#> Number of nonzero links: 2072 
#> Percentage nonzero weights: 13.2608 
#> Average number of links: 16.576 
#> Link number distribution:
#> 
#>  7 11 17 26 
#>  8 36 54 27 
#> 8 least connected regions:
#> 1 5 21 25 101 105 121 125 with 7 links
#> 27 most connected regions:
#> 32 33 34 37 38 39 42 43 44 57 58 59 62 63 64 67 68 69 82 83 84 87 88 89 92 93 94 with 26 links
if (require("sp", quietly=TRUE)) {
gt <- GridTopology(c(.125,.1), c(.25,.2), c(4L, 5L))
nb1 <- grid2nb(gt, queen = FALSE)
nb2 <- grid2nb(gt)

sg <- SpatialGrid(gt)
plot(sg, lwd=3)
plot(nb1, coordinates(sg), add=TRUE, lty=2, col=2, lwd=2)
plot(nb2, coordinates(sg), add=TRUE, lty=3, col=4)

str(grid2nb(d=5))
}

#> List of 5
#>  $ : int 2
#>  $ : int [1:2] 1 3
#>  $ : int [1:2] 2 4
#>  $ : int [1:2] 3 5
#>  $ : int 4
#>  - attr(*, "class")= chr "nb"