identify and count the size of individual patches in a binary matrix

patches.r

# identify and count the size of individual patches

patches <- function(x, state) {
  pattern <- x$cells
  pattern <- pattern %in% state
  map <- rep(NA, times = prod(x$dim))
  old <- rep(99, times = prod(x$dim)) 
  
  while(!identical(old[pattern], map[pattern])) {
    old <- map
    count = as.integer(1)
    for(i in which(pattern)) {
      neighbors <- map[x_with_border][x_to_evaluate[i]+interact]
      if(all(is.na(neighbors)) ) { 
        map[i] <- count
      } else {
        map[i] <- min(neighbors, na.rm = TRUE)
      }
      count <- count +1
    }
    
  }
  
  map <- as.factor(map)
  patchvec <- as.vector(sapply(levels(map), function(i) length(which(map == i) ) )) 
  
  out <- vector()
  if(length(patchvec) > 0) out <- sort(patchvec) else out <- NA
  #out <- data.frame(size = unique(out), freq = sapply(unique(out), function(i) length(which(out >= i)) ))
  return(out)
  
}