memory-safer

Author: rhijmans

R/layers.R

@@ -325,11 +325,15 @@ addRasterImage <- function(
 addRasterLegend <- function(map, x, layer = 1, ...) {
   stopifnot(inherits(x, "SpatRaster"))
   stopifnot(length(layer) == 1 && layer > 0 && layer <= terra::nlyr(x))
-
+  
+## might as well do this here and only once. Subsetting would otherwise have been necessary in 
+##  color_info <- base::subset(color_info, value %in% terra::values(x))
+  x <- x[[layer]]
+  
   # Retrieve the color table from the layer. If one doesn't exist, that means
   # the raster was colored some other way, like using colorFactor or something,
   # and the regular addLegend() is designed for those cases.
-  ct <- terra::coltab(x)[[layer]]
+  ct <- terra::coltab(x)[[1]]
   if (is.null(ct)) {
     stop("addRasterLegend() can only be used on layers with color tables (see ?terra::coltab). Otherwise, use addLegend().")
   }
@@ -341,10 +345,17 @@ addRasterLegend <- function(map, x, layer = 1, ...) {
     color = grDevices::rgb(ct$red/255, ct$green/255, ct$blue/255, ct$alpha/255)
   )
 
+  lvls <- terra::levels(x)[[1]]
+
   # Drop values that aren't part of the layer
-  color_info <- base::subset(color_info, value %in% terra::values(x))
+## unlike "values",  "unique" is memory-safe; it does not load all values 
+## into memory if the raster is large. So instead of:
+
+#  color_info <- base::subset(color_info, value %in% terra::values(x))
 
-  lvls <- terra::levels(x)[[layer]]
+## remove the levels to get the raw cell values
+  levels(x) <- NULL  
+  color_info <- base::subset(color_info, value %in% terra::unique(x)[[1]])
 
   res <- if (is.data.frame(lvls)) {
     # Use the labels from levels(x), and look up the matching colors in the