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Get the first value.

Source code

Description

This function has different behavior depending on arguments:

  • Missing -\> Takes first column of a context.
  • Character vectors -\> Syntactic sugar for pl$col(…)$first().

Usage

pl$first(...)

Arguments

… Characters indicating the column names (passed to pl$col(), see ?pl_col for details), or empty. If empty (default), returns an expression to take the first column of the context instead.

Value

Expr

See Also

  • \$first()

Examples

library("polars")

df = pl$DataFrame(
  a = c(1, 8, 3),
  b = c(4, 5, 2),
  c = c("foo", "bar", "foo")
)

df$select(pl$first())

#> shape: (3, 1)
#> ┌─────┐
#> │ a   │
#> │ --- │
#> │ f64 │
#> ╞═════╡
#> │ 1.0 │
#> │ 8.0 │
#> │ 3.0 │
#> └─────┘

df$select(pl$first("b"))

#> shape: (1, 1)
#> ┌─────┐
#> │ b   │
#> │ --- │
#> │ f64 │
#> ╞═════╡
#> │ 4.0 │
#> └─────┘

df$select(pl$first(c("a", "c")))

#> shape: (1, 2)
#> ┌─────┬─────┐
#> │ a   ┆ c   │
#> │ --- ┆ --- │
#> │ f64 ┆ str │
#> ╞═════╪═════╡
#> │ 1.0 ┆ foo │
#> └─────┴─────┘