Unpivot a Frame from wide to long format

Description

Usage

<LazyFrame>$melt(
  id_vars = NULL,
  value_vars = NULL,
  variable_name = NULL,
  value_name = NULL,
  ...,
  streamable = TRUE
)

Arguments

`id_vars`	Columns to use as identifier variables.
`value_vars`	Values to use as identifier variables. If `value_vars` is empty all columns that are not in `id_vars` will be used.
`variable_name`	Name to give to the new column containing the names of the melted columns. Defaults to "variable".
`value_name`	Name to give to the new column containing the values of the melted columns. Defaults to "value"
`…`	Not used.
`streamable`	Allow this node to run in the streaming engine. If this runs in streaming, the output of the melt operation will not have a stable ordering.

Details

Optionally leaves identifiers set.

This function is useful to massage a Frame into a format where one or more columns are identifier variables (id_vars), while all other columns, considered measured variables (value_vars), are "unpivoted" to the row axis, leaving just two non-identifier columns, ‘variable’ and ‘value’.

Value

A LazyFrame

Examples

library(polars)

lf = pl$LazyFrame(
  a = c("x", "y", "z"),
  b = c(1, 3, 5),
  c = c(2, 4, 6)
)
lf$melt(id_vars = "a", value_vars = c("b", "c"))$collect()

#> shape: (6, 3)
#> ┌─────┬──────────┬───────┐
#> │ a   ┆ variable ┆ value │
#> │ --- ┆ ---      ┆ ---   │
#> │ str ┆ str      ┆ f64   │
#> ╞═════╪══════════╪═══════╡
#> │ x   ┆ b        ┆ 1.0   │
#> │ y   ┆ b        ┆ 3.0   │
#> │ z   ┆ b        ┆ 5.0   │
#> │ x   ┆ c        ┆ 2.0   │
#> │ y   ┆ c        ┆ 4.0   │
#> │ z   ┆ c        ┆ 6.0   │
#> └─────┴──────────┴───────┘