for calculating the mode of a focal window over a categorical raster

focalmode.R

# for calculating the mode of a focal window over a categorical raster.
# Handling ties by retaining input cell value rather than default 'random'

winmode <- function(x) {
  y <- modal(x, na.rm = T, ties = 'NA')
  if (is.na(y)) { return(x[ceiling(length(x) / 2)]) } else {return(y)}}

# e.g.
# x <- raster(matrix(c(1:36), byrow = T, ncol = 6))
# f <- focal(x, w = matrix(1, ncol = 3, now = 3), fun = winmode)