as_mapper: Convert an object into a mapper function

In purrr: Functional Programming Tools

Convert an object into a mapper function

Description

as_mapper is the powerhouse behind the varied function specifications that most purrr functions allow. It is an S3 generic. The default method forwards its arguments to rlang::as_function().

Usage

as_mapper(.f, ...)

## S3 method for class 'character'
as_mapper(.f, ..., .null, .default = NULL)

## S3 method for class 'numeric'
as_mapper(.f, ..., .null, .default = NULL)

## S3 method for class 'list'
as_mapper(.f, ..., .null, .default = NULL)

Arguments

.f	A function, formula, or vector (not necessarily atomic). If a function, it is used as is. If a formula, e.g. ~ .x + 2, it is converted to a function. No longer recommended. If character vector, numeric vector, or list, it is converted to an extractor function. Character vectors index by name and numeric vectors index by position; use a list to index by position and name at different levels. If a component is not present, the value of .default will be returned.
...	Additional arguments passed on to methods.
.default, .null	Optional additional argument for extractor functions (i.e. when .f is character, integer, or list). Returned when value is absent (does not exist) or empty (has length 0). .null is deprecated; please use .default instead.

Examples

as_mapper(\(x) x + 1)
as_mapper(1)

as_mapper(c("a", "b", "c"))
# Equivalent to function(x) x[["a"]][["b"]][["c"]]

as_mapper(list(1, "a", 2))
# Equivalent to function(x) x[[1]][["a"]][[2]]

as_mapper(list(1, attr_getter("a")))
# Equivalent to function(x) attr(x[[1]], "a")

as_mapper(c("a", "b", "c"), .default = NA)

purrr documentation built on Aug. 8, 2025, 7:38 p.m.