Feature request: for SpatVector, return NULL for non-existent column

[dfriend21]

If you try to access a non-existent column on a SpatVector using $, an error is thrown. This differs from the default behavior of a data.frame, where NULL is returned. I've noticed this because I typically use is.null(df$column) to check if a column exists on a data frame, and therefore tried to use the same approach for a SpatVector. Personally, I think it'd be nice for the sake of consistency for a SpatVector to behave as a data.frame does in this case. However, there may be reasons to throw an error in this case rather than returning NULL - feel free to close this issue if this isn't how you want a SpatVector to behave.

library(terra)
#> terra 1.7.22

v <- vect(system.file("ex/lux.shp", package = "terra"))
v$not_a_column
#> Error: [$] not_a_column is not a variable name in x

v_df <- as.data.frame(v)
v_df$not_a_column
#> NULL

^{Created on 2023-04-17 with reprex v2.0.2}

[rhijmans]

it'd be nice for the sake of consistency for a SpatVector to behave as a data.frame

Of course, that is the intent. But it is easy to overlook details like this. Thanks for pointing that out.

I now get:

library(terra)
#terra 1.7.25
vect(cbind(0,0))$id
#NULL