R: Convert to function

as_function {rlang}

R Documentation

Convert to function

Description

as_function() transforms a one-sided formula into a function. This powers the lambda syntax in packages like purrr.

Usage

as_function(
  x,
  env = global_env(),
  ...,
  arg = caller_arg(x),
  call = caller_env()
)

is_lambda(x)

Arguments

`x`	A function or formula. If a function, it is used as is. If a formula, e.g. `~ .x + 2`, it is converted to a function with up to two arguments: `.x` (single argument) or `.x` and `.y` (two arguments). The `.` placeholder can be used instead of `.x`. This allows you to create very compact anonymous functions (lambdas) with up to two inputs. Functions created from formulas have a special class. Use `is_lambda()` to test for it. If a string, the function is looked up in `env`. Note that this interface is strictly for user convenience because of the scoping issues involved. Package developers should avoid supplying functions by name and instead supply them by value.
`env`	Environment in which to fetch the function in case `x` is a string.
`...`	These dots are for future extensions and must be empty.
`arg`	An argument name as a string. This argument will be mentioned in error messages as the input that is at the origin of a problem.
`call`	The execution environment of a currently running function, e.g. `caller_env()`. The function will be mentioned in error messages as the source of the error. See the `call` argument of `abort()` for more information.

Examples

f <- as_function(~ .x + 1)
f(10)

g <- as_function(~ -1 * .)
g(4)

h <- as_function(~ .x - .y)
h(6, 3)

# Functions created from a formula have a special class:
is_lambda(f)
is_lambda(as_function(function() "foo"))

[Package rlang version 1.0.2 Index]