R: Convert to function or closure

as_function {rlang}

R Documentation

Convert to function or closure

Description

as_function() transforms a one-sided formula into a function. This powers the lambda syntax in packages like purrr.
as_closure() first passes its argument to as_function(). If the result is a primitive function, it regularises it to a proper closure (see is_function() about primitive functions).

Usage

as_function(x, env = caller_env())

is_lambda(x)

as_closure(x, env = caller_env())

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 with up to two inputs. Functions created from formulas have a special class. Use is_lambda() to test for it.

env

Environment in which to fetch the function in case x is a string.

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"))

# Primitive functions are regularised as closures
as_closure(list)
as_closure("list")

# Operators have `.x` and `.y` as arguments, just like lambda
# functions created with the formula syntax:
as_closure(`+`)
as_closure(`~`)

[Package rlang version 0.4.0 Index]