Description Usage Arguments Details Value Author(s) Examples

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

1 2 3 |

`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 neigborhood matrix (see Details) |

`pairs` |
logical. If |

`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.

Robert J. Hijmans and Jacob van Etten

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 | ```
r <- raster(nrows=10, ncols=10)
adjacent(r, cells=c(1, 55), directions=8, pairs=TRUE)
a <- adjacent(r, cell = c(1,55,90), directions=4, sorted=TRUE)
a
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)
# 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
# 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))
``` |

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