as.data.table.data.frame keep.rownames & key

[MichaelChirico]

This works fine:

as.data.table(mtcars, keep.rownames = TRUE, key = 'rn')

But it's a bit arcane to know that rn is going to be the rownames' name. More readable might be:

as.data.table(mtcars, keep.rownames = 'model', key = 'model'

But that's an error:

Error in setkeyv(ans, key) : some columns are not in the data.table: model

Haven't looked yet but it must be setkeyv is applied before the setnames.

Note that this approach already works for setDT:

setDT(DT, keep.rownames = 'model', key = 'model')

[moodymudskipper]

It might add confusion, but thinking out loud maybe key = TRUE could use the row names as a key by default, or the first column if no row names (the id column will usually be first). This way your first call could be abbreviated to as.data.table(mtcars, key = TRUE)

[MichaelChirico]

Hmm but when I read as.data.table(mtcars, key=TRUE), actually I think of the answer being setkey(as.data.tabel(mtcars)); setkey keys on all columns by default.

[moodymudskipper]

Right, there could also be special values for key but that might be too much potential confusion to spare a few characters.