Generate neighbours list for grid cells

The function generates a list of neighbours for a grid of cells. Helper functions are used to convert to and from the vector indices for row and column grid positions, and rook (shared edge) or queen (shared edge or vertex) neighbour definitions are applied by type. If torus is TRUE, the grid is mapped onto a torus, removing edge effects.

Usage

cell2nb(nrow, ncol, type="rook", torus=FALSE, legacy=FALSE, x=NULL)
vi2mrc(i, nrow, ncol)

Arguments

nrow: number of rows in the grid, may also be an object inheriting from class "SpatialGrid" or "GridTopology" only in cell2nb
ncol: number of columns in the grid; if nrow or x is an object inheriting from class "SpatialGrid" or "GridTopology", it may be omitted
type: default rook, may also be queen
torus: default FALSE, if TRUE map grid onto torus
legacy: default FALSE, nrow/ncol reversed, if TRUE wrong col/row directions (see https://github.com/r-spatial/spdep/issues/20)
x: if given, an object inheriting from class "SpatialGrid" or "GridTopology", and replaces nrow and ncol
i: vector of vector indices corresponding to rowcol, a matrix with two columns of row, column indices

Value

The function returns an object of class nb with a list of integer vectors containing neighbour region number ids. See card for details of “nb” objects.

Author

Roger Bivand Roger.Bivand@nhh.no

Examples

nb7rt <- cell2nb(7, 7)
summary(nb7rt)
#> Neighbour list object:
#> Number of regions: 49 
#> Number of nonzero links: 168 
#> Percentage nonzero weights: 6.997085 
#> Average number of links: 3.428571 
#> Link number distribution:
#> 
#>  2  3  4 
#>  4 20 25 
#> 4 least connected regions:
#> 1:1 7:1 1:7 7:7 with 2 links
#> 25 most connected regions:
#> 2:2 3:2 4:2 5:2 6:2 2:3 3:3 4:3 5:3 6:3 2:4 3:4 4:4 5:4 6:4 2:5 3:5 4:5 5:5 6:5 2:6 3:6 4:6 5:6 6:6 with 4 links
xyc <- attr(nb7rt, "region.id")
xy <- matrix(as.integer(unlist(strsplit(xyc, ":"))), ncol=2, byrow=TRUE)
plot(nb7rt, xy)

nb7rt <- cell2nb(7, 7, torus=TRUE)
summary(nb7rt)
#> Neighbour list object:
#> Number of regions: 49 
#> Number of nonzero links: 196 
#> Percentage nonzero weights: 8.163265 
#> Average number of links: 4 
#> Link number distribution:
#> 
#>  4 
#> 49 
#> 49 least connected regions:
#> 1:1 2:1 3:1 4:1 5:1 6:1 7:1 1:2 2:2 3:2 4:2 5:2 6:2 7:2 1:3 2:3 3:3 4:3 5:3 6:3 7:3 1:4 2:4 3:4 4:4 5:4 6:4 7:4 1:5 2:5 3:5 4:5 5:5 6:5 7:5 1:6 2:6 3:6 4:6 5:6 6:6 7:6 1:7 2:7 3:7 4:7 5:7 6:7 7:7 with 4 links
#> 49 most connected regions:
#> 1:1 2:1 3:1 4:1 5:1 6:1 7:1 1:2 2:2 3:2 4:2 5:2 6:2 7:2 1:3 2:3 3:3 4:3 5:3 6:3 7:3 1:4 2:4 3:4 4:4 5:4 6:4 7:4 1:5 2:5 3:5 4:5 5:5 6:5 7:5 1:6 2:6 3:6 4:6 5:6 6:6 7:6 1:7 2:7 3:7 4:7 5:7 6:7 7:7 with 4 links
run <- FALSE
if (require("sp", quietly=TRUE)) run <- TRUE
if (run) {
# https://github.com/r-spatial/spdep/issues/20
GT <- GridTopology(c(1, 1), c(1, 1), c(10, 50))
SPix <- as(SpatialGrid(GT), "SpatialPixels")
nb_rook_cont <- poly2nb(as(SPix, "SpatialPolygons"), queen=FALSE)
nb_rook_dist <- dnearneigh(coordinates(SPix), 0, 1.01)
all.equal(nb_rook_cont, nb_rook_dist, check.attributes=FALSE)
## [1] TRUE
}
#> [1] TRUE
if (run) {
t.nb <- cell2nb(GT, type='rook', legacy=TRUE)
isTRUE(all.equal(nb_rook_cont, t.nb, check.attributes=FALSE))
## [1] FALSE
}
#> [1] FALSE
if (run) {
t.nb <- cell2nb(GT, type='rook')
isTRUE(all.equal(nb_rook_cont, t.nb, check.attributes=FALSE))
## [1] TRUE
}
#> [1] TRUE
if (run) {
# https://github.com/r-spatial/spdep/issues/55
# problem reported in issue caused by rep() cycling in unexpected order
GT <- GridTopology(c(1, 1), c(1, 1), c(22, 11))
SPix <- as(SpatialGrid(GT), "SpatialPixels")
nb_rook_cont <- poly2nb(as(SPix, "SpatialPolygons"), queen=FALSE)
nb_rook_dist <- dnearneigh(coordinates(SPix), 0, 1.01)
all.equal(nb_rook_cont, nb_rook_dist, check.attributes=FALSE)
}
#> [1] TRUE
if (run) {
t.nb <- cell2nb(GT, type='rook', legacy=TRUE)
isTRUE(all.equal(nb_rook_cont, t.nb, check.attributes=FALSE))
## [1] FALSE
}
#> [1] FALSE
if (run) {
t.nb <- cell2nb(GT, type='rook', legacy=FALSE)
isTRUE(all.equal(nb_rook_cont, t.nb, check.attributes=FALSE))
## [1] TRUE
}
#> [1] TRUE