Looping area calculations for multiple rasters in R

Question

The following code works great on individual rasters and gives me the information that I want:

r<-rast("LuckSpring_2001.tif")
activeCat(r)<-"Class_name"
r

f <- freq(r)
f$area <- f$count * 0.00009
f$percent = round(100 * f$area / sum(f$area), 1)
f

I'm wondering if there is a way to loop this code so I can apply it to multiple rasters and not have to do them all individually. A note that my rasters have different extents and class names.

Answer 1

You can do this by reading the rasters into a list object then iterating through the resulting list, defining a function that operates on each raster.

This creates the list object containing rasters.

rasters <- lapply(list.files(getwd(), pattern="tif$", 
                  full.names=TRUE), rast)

Now, we can operate on the list using lapply as our iterator and bind the results together.

results <- lapply(rasters, function(r) {
  activeCat(r) <- "Class_name"
  f <- freq(r)
  f$area <- f$count * res(r)[1]
  f$percent <- round(f$area / sum(f$area) * 100, 0))
})
( results <- do.call(rbind, results) )

Answer 2

I figured it out! Putting the code that worked for me here in case anybody else wants it.

    # Define the list of raster files 
    raster_files <- list.files(path=("C:/Users/"), pattern='\\.tif$', 
    full.names=TRUE)

    # Initialize an empty list to store the results
    result_list <- list()

    # Loop over each raster file
    for (file in raster_files) {
    # Read the raster file
    r <- rast(file)
    # Set the active category to "Class_name"
    activeCat(r) <- "Class_name"
    # Calculate frequency and area
    f <- freq(r)
    f$area <- f$count * 0.0009 #this number changes depending on resolution 
    f$percent <- round(100 * f$area / sum(f$area), 1)
    result_list[[file]] <- f
    }

    #List results
    for (i in seq_along(result_list)) {
    cat("Raster File:", names(result_list)[i], "\n")
    print(result_list[[I]])
    cat("\n")
    }

    #This makes a results table
    result_table <- bind_rows(result_list, .id = "raster_name")'