spdep (version 0.8-1)

cell2nb: Generate neighbours list for grid cells

Description

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)
mrc2vi(rowcol, nrow, ncol)
rookcell(rowcol, nrow, ncol, torus=FALSE, rmin=1, cmin=1)
queencell(rowcol, nrow, ncol, torus=FALSE, rmin=1, cmin=1)
vi2mrc(i, nrow, ncol)

Arguments

nrow

number of rows in the grid

ncol

number of columns in the grid

type

rook or queen

torus

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)

rowcol

matrix with two columns of row, column indices

i

vector of vector indices corresponding to rowcol

rmin

lowest row index

cmin

lowset column index

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.

See Also

summary.nb, card

Examples

# NOT RUN {
nb7rt <- cell2nb(7, 7)
summary(nb7rt)
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)
# 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
t.nb <- cell2nb(nrow=50, ncol=10, type='rook', legacy=TRUE)
isTRUE(all.equal(nb_rook_cont, t.nb, check.attributes=FALSE))
## [1] FALSE
t.nb <- cell2nb(nrow=50, ncol=10, type='rook')
isTRUE(all.equal(nb_rook_cont, t.nb, check.attributes=FALSE))
## [1] TRUE
# }