Obtain a RasterLayer or the cells of RasterLayer that are equal to or lie within a range of specified values

This function obtains a RasterLayer or the cells of a RasterLayer that are equal to a specified value or lie within a specified range of values. To implement this function, a raster (x) and a value or range of values (y) for which a RasterLayer or the numbers of cells corresponding to those values are desired must be supplied. If a range of values is supplied, an additional argument (interval) controls whether or not cells within and equal to or simply within the specified range are returned.

cells_from_val(x, y, interval = 1L, cells = TRUE, na.rm = TRUE)

Arguments

x: A raster object.
y: A number or a vector with two numbers representing the lower and upper boundaries of the interval of values within which cells are identified.
interval: If y is a vector of length two, interval is an integer that controls whether or not to query cells within and equal to (interval = 1L) or simply within (interval = 2L) the range specified by y.
cells: A logical variable that defines whether or not to return a vector of cell numbers (TRUE) or a RasterLayer of the cells corresponding to y.
na.rm: A logical variable that defines whether or not to ignore NAs.

Value

The function returns a RasterLayer (if cells = FALSE) or an integer vector of numbers (if cells = TRUE) that defines the cells that are equal to, or lie within, specified value(s) y.

Author

Edward Lavender

Examples

# Define an example RasterLayer
ncl <- 10
nrw <- 10
n <- ncl * nrw
mat <- matrix(1:n, ncol = ncl, nrow = nrw, byrow = TRUE)
r <- raster::raster(mat)
# Visualise example RasterLayer
raster::plot(r)
raster::text(r)

# Obtain the number(s) of cells corresponding to a particular value
cells_from_val(r, 1)
#> [1] 1
# Obtain a RasterLayer of the cells corresponding to a particular value
r1 <- cells_from_val(r, 1, cells = FALSE)
raster::plot(r1)

# Obtain the number(s) of cells within or equal to a range of values
cells_from_val(r, c(1, 10))
#>  [1]  1  2  3  4  5  6  7  8  9 10
# Obtain the number(s) of cells within a range of values
cells_from_val(r, c(1, 10), interval = 2L)
#> [1] 2 3 4 5 6 7 8 9
# As above but returning a raster layer
cells_from_val(r, c(1, 10), interval = 2L, cells = FALSE)
#> class      : RasterLayer 
#> dimensions : 10, 10, 100  (nrow, ncol, ncell)
#> resolution : 0.1, 0.1  (x, y)
#> extent     : 0, 1, 0, 1  (xmin, xmax, ymin, ymax)
#> crs        : NA 
#> source     : memory
#> names      : layer 
#> values     : 0, 1  (min, max)
#>