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Apply a custom R function to a whole Series or sequence of Series.

Source code

Description

[Experimental]

The output of this custom function is presumed to be either a Series, or an R vector that will be converted into a Series by as_polars_series().

Usage

<Expr>$map_batches(lambda, return_dtype = NULL, ...)

Arguments

lambda Function to apply.
return_dtype Dtype of the output Series. It is recommended to set this whenever possible. If this is NULL, it tries to infer the datatype by calling the function with dummy data and looking at the output.
… These dots are for future extensions and must be empty.

Value

A polars expression

Examples

library("polars")

df <- pl$DataFrame(
  sine = c(0.0, 1.0, 0.0, -1.0),
  cosine = c(1.0, 0.0, -1.0, 0.0)
)
df$select(pl$all()$map_batches(\(x) {
  x$to_r_vector() |>
    which.max()
}))

#> shape: (1, 2)
#> ┌──────┬────────┐
#> │ sine ┆ cosine │
#> │ ---  ┆ ---    │
#> │ i32  ┆ i32    │
#> ╞══════╪════════╡
#> │ 2    ┆ 1      │
#> └──────┴────────┘

# Call a function that takes multiple arguments by creating a struct and
# referencing its fields inside the function call.
df <- pl$DataFrame(
  a = c(5, 1, 0, 3),
  b = c(4, 2, 3, 4),
)
df$with_columns(
  a_times_b = pl$struct("a", "b")$map_batches(
    \(x) x$struct$field("a") * x$struct$field("b")
  )
)

#> shape: (4, 3)
#> ┌─────┬─────┬───────────┐
#> │ a   ┆ b   ┆ a_times_b │
#> │ --- ┆ --- ┆ ---       │
#> │ f64 ┆ f64 ┆ f64       │
#> ╞═════╪═════╪═══════════╡
#> │ 5.0 ┆ 4.0 ┆ 20.0      │
#> │ 1.0 ┆ 2.0 ┆ 2.0       │
#> │ 0.0 ┆ 3.0 ┆ 0.0       │
#> │ 3.0 ┆ 4.0 ┆ 12.0      │
#> └─────┴─────┴───────────┘