Return the 8 neighbors, as cell numbers, of each cell on a raster.
ngb8(n_row, n_col)Integer. The number of rows of a Raster or object.
Integer. The number of columns of a Raster object.
Named list, the nth element of the list corresponds to the 8
adjacent cell numbers of the nth cell on the Raster* object.
A cell with coordinates (x, y) has 8 neighbors with
coordinates: (x±1, y), (x, y±1) and (x±1, y±1). Cells
on the edge of a raster have less than 8 neighbors. The function identifies
the neighbors of a cell as cell numbers.
## Matrix m mocking a raster of 3 rows and 4 columns
m <- matrix(1:12, nrow = 3, ncol = 4, byrow = TRUE)
m
#> [,1] [,2] [,3] [,4]
#> [1,] 1 2 3 4
#> [2,] 5 6 7 8
#> [3,] 9 10 11 12
nbs <- ngb8(3, 4)
nbs
#> $`1`
#> [1] 2 5 6
#>
#> $`2`
#> [1] 1 3 5 6 7
#>
#> $`3`
#> [1] 2 4 6 7 8
#>
#> $`4`
#> [1] 3 7 8
#>
#> $`5`
#> [1] 1 2 6 9 10
#>
#> $`6`
#> [1] 1 2 3 5 7 9 10 11
#>
#> $`7`
#> [1] 2 3 4 6 8 10 11 12
#>
#> $`8`
#> [1] 3 4 7 11 12
#>
#> $`9`
#> [1] 5 6 10
#>
#> $`10`
#> [1] 5 6 7 9 11
#>
#> $`11`
#> [1] 6 7 8 10 12
#>
#> $`12`
#> [1] 7 8 11
#>