Run any polars expression on the sub-array’s values

Description

Usage

<Expr>$arr$eval(expr, ..., as_list = FALSE)

Arguments

expr Expression to run. Note that you can select an element with pl$element(), pl$first(), and more. See Examples.

… These dots are for future extensions and must be empty.

as_list Collect the resulting data into a list datatype (instead of array datatype). This allows for expressions which output a variable amount of data.

Value

A polars expression

Examples

library("polars")

df <- pl$DataFrame(
  a = list(c(1, 1), c(8, 5), c(3, 2))
)$cast(pl$Array(pl$Float64, 2))

df$with_columns(
  cum_sum = pl$col("a")$arr$eval(pl$element()$cum_sum())
)

#> shape: (3, 2)
#> ┌───────────────┬───────────────┐
#> │ a             ┆ cum_sum       │
#> │ ---           ┆ ---           │
#> │ array[f64, 2] ┆ array[f64, 2] │
#> ╞═══════════════╪═══════════════╡
#> │ [1.0, 1.0]    ┆ [1.0, 2.0]    │
#> │ [8.0, 5.0]    ┆ [8.0, 13.0]   │
#> │ [3.0, 2.0]    ┆ [3.0, 5.0]    │
#> └───────────────┴───────────────┘

# This would error without `as_list = TRUE` since `$unique()` doesn't return
# the same number of values in each row.
df$with_columns(
  cum_sum = pl$col("a")$arr$eval(pl$element()$unique(), as_list = TRUE)
)

#> shape: (3, 2)
#> ┌───────────────┬────────────┐
#> │ a             ┆ cum_sum    │
#> │ ---           ┆ ---        │
#> │ array[f64, 2] ┆ list[f64]  │
#> ╞═══════════════╪════════════╡
#> │ [1.0, 1.0]    ┆ [1.0]      │
#> │ [8.0, 5.0]    ┆ [8.0, 5.0] │
#> │ [3.0, 2.0]    ┆ [3.0, 2.0] │
#> └───────────────┴────────────┘