Operations on Polars grouped DataFrame

Description

The GroupBy class in R, is just another interface on top of the DataFrame in rust polars. Groupby does not use the rust api for \<DataFrame>$group_by() + $agg() because the groupby-struct is a reference to a DataFrame and that reference will share lifetime with its parent DataFrame.

Details

There is no way to expose lifetime limited objects via extendr currently (might be quirky anyhow with R GC). Instead the inputs for the group_by are just stored on R side, until also agg is called. Which will end up in a self-owned DataFrame object and all is fine. groupby aggs are performed via the rust polars LazyGroupBy methods, see DataFrame.groupby_agg method.

Active bindings

columns

$columns returns a character vector with the column names.

Examples

library("polars")

as_polars_df(mtcars)$group_by("cyl")$agg(
  pl$col("mpg")$sum()
)

#> shape: (3, 2)
#> ┌─────┬───────┐
#> │ cyl ┆ mpg   │
#> │ --- ┆ ---   │
#> │ f64 ┆ f64   │
#> ╞═════╪═══════╡
#> │ 8.0 ┆ 211.4 │
#> │ 6.0 ┆ 138.2 │
#> │ 4.0 ┆ 293.3 │
#> └─────┴───────┘