as_function {rlang}R Documentation

Convert to function or closure

Description

Stable lifecycle

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

Lambdas currently do not support quasiquotation, due to the way the arguments are handled internally.

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(`~`)

# Use a regular function for tidy evaluation, also when calling functions
# that use tidy evaluation:
## Bad:
e <- as_function(~ as_label(ensym(.x)))
## Good:
e <- as_function(function(x) as_label(ensym(x)))

e(y)

[Package rlang version 0.4.1 Index]