`adjacent.Rd`

Identify cells that are adjacent to a set of cells on a raster.

```
# S4 method for BasicRaster
adjacent(x, cells, directions=4, pairs=TRUE, target=NULL, sorted=FALSE,
include=FALSE, id=FALSE, ...)
```

- x
Raster* object

- cells
vector of cell numbers for which adjacent cells should be found. Cell numbers start with 1 in the upper-left corner and increase from left to right and from top to bottom

- directions
the number of directions in which cells should be connected: 4 (rook's case), 8 (queen's case), 16 (knight and one-cell queen moves), or 'bishop' to connect cells with one-cell diagonal moves. Or a neighborhood matrix (see Details)

- pairs
logical. If

`TRUE`

, a matrix of pairs of adjacent cells is returned. If`FALSE`

, a vector of cells adjacent to`cells`

is returned- target
optional vector of target cell numbers that should be considered. All other adjacent cells are ignored

- sorted
logical. Should the results be sorted?

- include
logical. Should the focal cells be included in the result?

- id
logical. Should the id of the cells be included in the result? (numbered from 1 to length(cells)

- ...
additional arguments. None implemented

A neighborhood matrix identifies the cells around each cell that are considered adjacent. The matrix should have one, and only one, cell with value 0 (the focal cell); at least one cell with value 1 (the adjacent cell(s)); All other cells are not considered adjacent and ignored.

matrix or vector with adjacent cells.

```
r <- raster(nrows=10, ncols=10)
adjacent(r, cells=c(1, 55), directions=8, pairs=TRUE)
#> from to
#> [1,] 55 44
#> [2,] 1 10
#> [3,] 55 54
#> [4,] 1 20
#> [5,] 55 64
#> [6,] 55 46
#> [7,] 1 2
#> [8,] 55 56
#> [9,] 1 12
#> [10,] 55 66
#> [11,] 55 45
#> [12,] 1 11
#> [13,] 55 65
a <- adjacent(r, cell = c(1,55,90), directions=4, sorted=TRUE)
a
#> from to
#> [1,] 1 2
#> [2,] 1 10
#> [3,] 1 11
#> [4,] 55 45
#> [5,] 55 54
#> [6,] 55 56
#> [7,] 55 65
#> [8,] 90 80
#> [9,] 90 81
#> [10,] 90 89
#> [11,] 90 100
r[c(1,55,90)] <- 1
r[a] <- 2
plot(r)
# same result as above
rook <- matrix(c(NA, 1, NA,
1, 0, 1,
NA, 1, NA), ncol=3, byrow=TRUE)
adjacent(r, cells = c(1,55,90), directions=rook, sorted=TRUE)
#> from to
#> [1,] 1 2
#> [2,] 1 10
#> [3,] 1 11
#> [4,] 55 45
#> [5,] 55 54
#> [6,] 55 56
#> [7,] 55 65
#> [8,] 90 80
#> [9,] 90 81
#> [10,] 90 89
#> [11,] 90 100
# Count the number of times that a cell with a certain value
# occurs next to a cell with a certain value
set.seed(0)
r <- raster(ncol=10, nrow=10)
values(r) <- round(runif(ncell(r)) * 5)
a <- adjacent(r, 1:ncell(r), 4, pairs=TRUE)
tb <- table(r[a[,1]], r[a[,2]])
tb
#>
#> 0 1 2 3 4 5
#> 0 2 4 7 4 10 0
#> 1 4 14 14 7 19 6
#> 2 7 14 30 15 35 8
#> 3 4 7 15 14 13 3
#> 4 10 19 35 13 20 5
#> 5 0 6 8 3 5 0
# make a matrix out of the 'table' object
tb <- unclass(tb)
plot(raster(tb, xmn=-0.5, xmx=5.5, ymn=-0.5, ymx=5.5))
```