raster (version 2.0-41)

adjacency: Pairs of adjacent cells

Description

Identify pairs of cells that are adjacent. See adjacent for an alternative implementation.

Usage

adjacency(x, fromCells, toCells, directions)

Arguments

x

Raster* object

fromCells

a vector of cell numbers for which adjacent cells should be calculated

toCells

a vector of cell numbers from which adjacent cells are selected. You can use the adjacent function if you want all cells to be considered

directions

in how many direction cells should be connected: 4, 8 or 16; or "bishop"

Value

• A two column matrix with each row containing a pair of adjacent cells.

See Also

adjacent

Examples

r <- raster(nrows=10, ncols=10)
adj <- adjacency(r, fromCells = c(1,30,55,72,100), 
				toCells = 1:ncell(r), directions=4) 
	
# put the result in a RasterLayer
r[] <- 0
r[c(1,30,55,72,100)] <- 1
r[adj[,2]] <- 2
plot(r)


# How many time does one cell value occur next to another cell value?
r <- raster(ncol=10, nrow=10)
set.seed(0)
r[] <- round(runif(ncell(r)) * 5)
a <- adjacency(r, 1:ncell(r), 1:ncell(r), 8)
v1 <- r[a[,1]]
v2 <- r[a[,2]]
m <- matrix(0, nrow=5,ncol=5)
for(i in 1:length(v1)) {m[v1[i], v2[i]] <- m[v1[i], v2[i]] +1}
m