Feature request: `n_distinct()` implementation w/ multiple arguments.

[lschneiderbauer]

Hi,

I understand that n_distinct() with multiple arguments is not supported for a generic dbplyr backend since SQL does not support that out of the box.

Is it possible to implement it in the case of duckdb using structs?

For example:

dbplyr::tbl_lazy(data.frame(x = 1, y = 1), duckdb::simulate_duckdb()) |>
summarize(l = n_distinct(x, y))

could be translated to

<SQL>
SELECT COUNT(DISTINCT {'x' : `x`, 'y' : `y`}) AS `l`
FROM `df`

which executes on duckdb.

[krlmlr]

Thanks, good idea! Would you like to contribute? I think the relevant code is in https://github.com/duckdb/duckdb-r/blob/main/R/backend-dbplyr__duckdb_connection.R .

[github-actions]

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