How to add layer name in the output of expanse function using terra package?

[bappa10085]

I want to add the layer name in place of layer number in the output of expanse function using terra r package. Here is a reproducible example

library(terra)

# first create a raster
r1 <- r2 <- r3 <- rast(nrow=10, ncol=10)
# Assign random cell values
values(r1) <- runif(ncell(r1))
values(r2) <- runif(ncell(r2))
values(r3) <- runif(ncell(r3))
s <- c(r1, r2, r3)
names(s) <- c("a", "b", "c")
# classify the values into four groups
m <- c(0, 0.1, 1,
       0.1, 0.3, 2,
       0.3, 0.6, 3,
       0.6, 1, 4)

#Reclassify the raster stack
rclmat <- matrix(m, ncol=3, byrow=TRUE)
rc <- classify(s, rclmat, include.lowest=TRUE)

#Calculate frequency of pixels under each class
expanse(rc, unit="km", byValue = T)

As you can see from the output layer represents the layer number. Now how to add layer name in the output of expanse function using terra package?

[kadyb]

I think this is not implemented yet, but for now you can just merge the layer number with its name.

df = expanse(rc, unit="km", byValue = T)
layer_names = data.frame(layer = seq_along(names(rc)), name = names(rc))
df = merge(df, layer_names, by = "layer")

[bappa10085]

Thank you very much for such a quick reply. It will be great to have an argument like usenames = T in the freq function.

[rhijmans]

with

e <- expanse(rc, unit="km", byValue = T)

You can do

e$name <- names(rc)[e$layer]

or

e$layer <- names(rc)[e$layer]

But I have now also added argument usenames as suggested such that you can do

expanse(rc, unit="km", byValue = T, usenames=T) |> head()
#  layer value      area
#1     a     1  47081113
#2     a     2  95712302
#3     a     3 163637536
#4     a     4 203634669
#5     b     1  82867639
#6     b     2  61724915