Get the value by index in every sub-array

Description

This allows to extract one value per array only. Values are 0-indexed (so index 0 would return the first item of every sub-array) and negative values start from the end (so index -1 returns the last item).

Usage

<Expr>$arr$get(index, ..., null_on_oob = TRUE)

Arguments

index	An Expr or something coercible to an Expr, that must return a single index.
…	These dots are for future extensions and must be empty.
null_on_oob	If TRUE, return null if an index is out of bounds. Otherwise, raise an error.

Value

A polars expression

Examples

library("polars")

df <- pl$DataFrame(
  values = list(c(1, 2), c(3, 4), c(NA, 6)),
  idx = c(1, NA, 3)
)$cast(values = pl$Array(pl$Float64, 2))
df$with_columns(
  using_expr = pl$col("values")$arr$get("idx"),
  val_0 = pl$col("values")$arr$get(0),
  val_minus_1 = pl$col("values")$arr$get(-1),
  val_oob = pl$col("values")$arr$get(10)
)

#> shape: (3, 6)
#> ┌───────────────┬──────┬────────────┬───────┬─────────────┬─────────┐
#> │ values        ┆ idx  ┆ using_expr ┆ val_0 ┆ val_minus_1 ┆ val_oob │
#> │ ---           ┆ ---  ┆ ---        ┆ ---   ┆ ---         ┆ ---     │
#> │ array[f64, 2] ┆ f64  ┆ f64        ┆ f64   ┆ f64         ┆ f64     │
#> ╞═══════════════╪══════╪════════════╪═══════╪═════════════╪═════════╡
#> │ [1.0, 2.0]    ┆ 1.0  ┆ 2.0        ┆ 1.0   ┆ 2.0         ┆ null    │
#> │ [3.0, 4.0]    ┆ null ┆ null       ┆ 3.0   ┆ 4.0         ┆ null    │
#> │ [null, 6.0]   ┆ 3.0  ┆ null       ┆ null  ┆ 6.0         ┆ null    │
#> └───────────────┴──────┴────────────┴───────┴─────────────┴─────────┘