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rlegendterra

Reorder plot legend categories in a terra SpatVector map

Is there a way to have the plot legend categories in a specific order with a SpatVector map of package terra? Example:

library(terra)
v <- vect(system.file("ex/lux.shp", package="terra"))
head(v)
plot(v, "NAME_1")

enter image description here

How can we get "Luxembourg" to appear first in the legend, and also the remaining categories in a user-specified order? We've tried converting the "NAME_1" column to factor, but it's still interpreted as character.

Solution

  • You can use the argument sort=FALSE. In that case, the legend will be in the same order as what is returned by unique("fieldname")

    Example data

    library(terra)
v <- vect(system.file("ex/lux.shp", package="terra"))

    If we wanted to map "NAME_1" alphabetically, except with "Luxembourg" on top, you could do

    # make sure names are sorted 
v <- v[order(v$NAME_1), ]
# put Luxembourg on top
vv <- rbind(v[v$NAME_1 == "Luxembourg", ], v[v$NAME_1 != "Luxembourg", ])

plot(vv, "NAME_1", sort=FALSE)

    enter image description here

    terra version 1.5.38 (currently the development version) now has these two additional options:

    Sort in decreasing order

    plot(v, "NAME_2", decreasing=TRUE)

    enter image description here

    Sort in a specified order (or random, as in this example)

    set.seed(66)
u <- unique(v$NAME_2) |> sample()
plot(v, "NAME_2", sort=u)

    enter image description here