[R-sig-Geo] Count frequency in raster stacks

[Lyndon Estes]

Hi Thiago,

Something like this should work:

s <- stack(lapply(1:5, function(x) {
  r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)
  r[] <- round(runif(22 * 20, min=0, max=600), digits=0)
  r
}))

intervals <- seq(0, 600, 100)

vals <- sapply(1:nlayers(s), function(x) {  # x <- 1
  # Count frequencies and calculate percentage
  ## note: don't use df or t as object names--they are both functions
  tab <- table(cut(as.vector(s[[x]]), intervals, include.lowest=TRUE))
  # ncells <- length(Which(!is.na(s[[x]]), cells = TRUE)) # alternative
  ncells <- sum(!is.na(s[[x]][]))
  DF <- data.frame(round(tab, digits=2))[, 2]
})

# set up a column that decribes the rainfall bins/intervals
ints <- cbind(intervals[-length(intervals)], intervals[-1])
bins <- apply(ints, 1, function(x) paste(x, collapse = "-"))

# bind to output
cbind.data.frame(bins, vals)


On Wed, Feb 17, 2016 at 4:27 AM Thiago V. dos Santos <
thi_veloso at yahoo.com.br> wrote:

> Hi all,
>
> I am trying to count the frequency of values in raster objects based on
> specified intervals. For example, I have a raster storing monthly rainfall
> totals ranging from 50 to 600 mm. And I need to know how many values fall
> in the interval 0-100, how many on 101-200, 201-300 and so on.
>
> I managed to do it in a single raster:
>
> require(raster)
>
> ## scratch a raster and fill some random values
> r <- raster(nrows=22, ncols=20, xmn=-58, xmx=-48, ymn=-33, ymx=-22)
> r[] <- round(runif(22 * 20, min=0, max=600), digits=0)
>
> # Count raster cells (excluding NA's) and set intervals
> ncells <- sum(!is.na(r[]))
> intervals <- seq(0, 600, 100)
>
> # Count frequencies and calculate percentage
> t <- table(cut(as.vector(r), intervals, include.lowest=TRUE)) / ncells *
> 100
> df <- data.frame(round(t, digits=2))
>
>
> However, how can I do the same for a raster stack, storing the count of
> each layer in a column of the resulting data frame?
> Thanks in advance,
>  -- Thiago V. dos Santos
>
> PhD student
> Land and Atmospheric Science
> University of Minnesota
>
> _______________________________________________
> R-sig-Geo mailing list
> R-sig-Geo at r-project.org
> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>

	[[alternative HTML version deleted]]