Get the value by index in a list

Source code

Description

This allows to extract one value per list only. To extract several values by index, use $list$gather().

Usage

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

Arguments

index	An Expr or something coercible to an Expr, that must return a single index. Values are 0-indexed (so index 0 would return the first item of every sublist) and negative values start from the end (index -1 returns the last item).
…	Ignored.
null_on_oob	If TRUE, return null if an index is out of bounds. Otherwise, raise an error.

Value

Expr

Examples

library("polars")

df = pl$DataFrame(
  values = list(c(2, 2, NA), c(1, 2, 3), NA_real_, NULL),
  idx = c(1, 2, NA, 3)
)
df$with_columns(
  using_expr = pl$col("values")$list$get("idx"),
  val_0 = pl$col("values")$list$get(0),
  val_minus_1 = pl$col("values")$list$get(-1),
  val_oob = pl$col("values")$list$get(10)
)

#> shape: (4, 6)
#> ┌──────────────────┬──────┬────────────┬───────┬─────────────┬─────────┐
#> │ values           ┆ idx  ┆ using_expr ┆ val_0 ┆ val_minus_1 ┆ val_oob │
#> │ ---              ┆ ---  ┆ ---        ┆ ---   ┆ ---         ┆ ---     │
#> │ list[f64]        ┆ f64  ┆ f64        ┆ f64   ┆ f64         ┆ f64     │
#> ╞══════════════════╪══════╪════════════╪═══════╪═════════════╪═════════╡
#> │ [2.0, 2.0, null] ┆ 1.0  ┆ null       ┆ 2.0   ┆ null        ┆ null    │
#> │ [1.0, 2.0, 3.0]  ┆ 2.0  ┆ null       ┆ 1.0   ┆ 3.0         ┆ null    │
#> │ [null]           ┆ null ┆ null       ┆ null  ┆ null        ┆ null    │
#> │ []               ┆ 3.0  ┆ null       ┆ null  ┆ null        ┆ null    │
#> └──────────────────┴──────┴────────────┴───────┴─────────────┴─────────┘