CODEWITHSUNDEEP
rstackr-rastercalc
setfivor
setfivor

Reputation: 9

raster calculation with condition of each cell by layers in R

I have stack raster dataset with several layers, however, I want to calculate the sum of each cell with for different layer selection, and finally generate a new layer, anyone has some good suggestion by using calc or overlay or some other raster calculation in R? I can do by loops and make the calculation, but it will consume many times when I have many layers, and also use many of the storage, my script as follows,

## library(raster)
make_calc <- function(rr, start, end) {
  rr <- as.array(rr)
  start <- as.array(start)
  end <- as.array(end)
  dms <- dim(raster)
  tmp <- array(NA, dim = dms[1:2])
  for (i in 1:dms[1]) {
    for (j in 1:dms[2]) {
      tmp[i,j] <- sum(raster[i,j,start[i,j,1]:end[i,j,1]], na.rm = TRUE)
    }
  }
  return(tmp)
}

rr <- raster(res = 10)
rr[] <- 1
rr <- stack(rr, rr, rr, rr)
start <- raster(res = 10)
start[] <- sample(1:2, ncell(start), replace = TRUE)
end <- raster(res = 10)
end[] <- sample(3:4, ncell(end), replace = TRUE)
result <- make_calc(rr, start, end)

Upvotes: 0

Views: 1587

Answers (1)

Jeffrey Evans
Jeffrey Evans

Reputation: 2417

Why are you coercing into arrays? You can easily collapse a raster into a vector but, that does not even seem necessary here. In the future, please try to be more clear on what your expected outcome is.

Based on your code, I really don't know what you are getting at. I am going to take a few guesses on summing specified rasters in the stack, drawing a random sample, across rasters to be summed and finally, drawing a random sample of cells to be summed.

For a sum on specified rasters in a stack, you can just index what you are after in the stack using a double bracket. In this case, rasters 1 and 3 in the stack would be the only ones summed. 

library(raster)
rr <- raster(res = 10)
rr[] <- 1
rr <- stack(rr, rr, rr, rr)

( sum_1_3 <- calc(rr[[c(1,3)]], sum) )

If you are wanting a random sample of the values across rasters, for every cell, you could write a function that is passed to calc. Here is an example that grabs a random sample of n size, across the raster layers values and sums them.

rs.sum <- function(x, n=2) {sum( x[sample(1:length(x),n)], na.rm=TRUE)} 
rs.sum.raster <- calc(rr, rs.sum)

If you are wanting to apply a function to a limited random selection of cells, you could create a random sample of the raster that would be used as an index. Here we create a random sample of cells, create an empty raster and pipe the sum of rasters 1 and 2 (in the stack) based on the random sample cell index. A raster in the stack is indexed using the double bracket and the raster values are indexed using a single bracket so, for raster 1 in the stack with limiting to the values in the random sample you would use: rr[[1]][rs] 

rs <- sample(1:ncell(rr[[1]]), 300)
r.sum <- rr[[1]]
r.sum[] <- NA
r.sum[rs] <- rr[[1]][rs] + rr[[2]][rs] 
  plot(r.sum)

Upvotes: 1

Related Questions