Return the number of rows in the context$

Description

This is similar to COUNT(*) in SQL.

Usage

pl$len()

Value

A polars expression

Examples

library("polars")

df <- pl$DataFrame(
  a = c(1, 2, NA),
  b = c(3, NA, NA),
  c = c("foo", "bar", "foo"),
)
df$select(pl$len())

#> shape: (1, 1)
#> ┌─────┐
#> │ len │
#> │ --- │
#> │ u32 │
#> ╞═════╡
#> │ 3   │
#> └─────┘

# Generate an index column by using len in conjunction with $int_range()
df$with_columns(
  pl$int_range(pl$len(), dtype = pl$UInt32)$alias("index")
)

#> shape: (3, 4)
#> ┌──────┬──────┬─────┬───────┐
#> │ a    ┆ b    ┆ c   ┆ index │
#> │ ---  ┆ ---  ┆ --- ┆ ---   │
#> │ f64  ┆ f64  ┆ str ┆ u32   │
#> ╞══════╪══════╪═════╪═══════╡
#> │ 1.0  ┆ 3.0  ┆ foo ┆ 0     │
#> │ 2.0  ┆ null ┆ bar ┆ 1     │
#> │ null ┆ null ┆ foo ┆ 2     │
#> └──────┴──────┴─────┴───────┘