Return the `k` largest rows

Description

Non-null elements are always preferred over null elements, regardless of the value of reverse. The output is not guaranteed to be in any particular order, call sort() after this function if you wish the output to be sorted.

Usage

<DataFrame>$top_k(k, ..., by, reverse = FALSE)

Arguments

k Number of rows to return.

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

by Column(s) used to determine the bottom rows. Accepts expression input. Strings are parsed as column names.

reverse Consider the k smallest elements of the by column(s) (instead of the k largest). This can be specified per column by passing a sequence of booleans.

Value

A polars DataFrame

Examples

library("polars")

df <- pl$DataFrame(
  a = c("a", "b", "a", "b", "b", "c"),
  b = c(2, 1, 1, 3, 2, 1)
)

# Get the rows which contain the 4 largest values in column b.
df$top_k(4, by = "b")

#> shape: (4, 2)
#> ┌─────┬─────┐
#> │ a   ┆ b   │
#> │ --- ┆ --- │
#> │ str ┆ f64 │
#> ╞═════╪═════╡
#> │ b   ┆ 3.0 │
#> │ a   ┆ 2.0 │
#> │ b   ┆ 2.0 │
#> │ b   ┆ 1.0 │
#> └─────┴─────┘

# Get the rows which contain the 4 largest values when sorting on column a
# and b
df$top_k(4, by = c("a", "b"))

#> shape: (4, 2)
#> ┌─────┬─────┐
#> │ a   ┆ b   │
#> │ --- ┆ --- │
#> │ str ┆ f64 │
#> ╞═════╪═════╡
#> │ c   ┆ 1.0 │
#> │ b   ┆ 3.0 │
#> │ b   ┆ 2.0 │
#> │ b   ┆ 1.0 │
#> └─────┴─────┘

Return the k largest rows