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Convert an object into a mapper function

Source: R/map-mapper.R
as_mapper.Rd

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, specified in one of the following ways:

  • A named function, e.g. mean.

  • An anonymous function, e.g. \(x) x + 1 or function(x) x + 1.

  • A string, integer, or list, e.g. "idx", 1, or list("idx", 1) which are converted to extractor functions, i.e. \(x) pluck(x, "idx"), \(x) pluck(x, 1), and \(x) pluck(x, "idx", 1) respectively. 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)
#> function (x) 
#> x + 1
#> <environment: 0x55da2e4365f0>
as_mapper(1)
#> function (x, ...) 
#> pluck_raw(x, list(1), .default = NULL)
#> <environment: 0x55da2e3d3530>

as_mapper(c("a", "b", "c"))
#> function (x, ...) 
#> pluck_raw(x, list("a", "b", "c"), .default = NULL)
#> <environment: 0x55da2e36c758>
# Equivalent to function(x) x[["a"]][["b"]][["c"]]

as_mapper(list(1, "a", 2))
#> function (x, ...) 
#> pluck_raw(x, list(1, "a", 2), .default = NULL)
#> <environment: 0x55da2e2f9bb0>
# Equivalent to function(x) x[[1]][["a"]][[2]]

as_mapper(list(1, attr_getter("a")))
#> function (x, ...) 
#> pluck_raw(x, list(1, function (x) 
#> attr(x, attr, exact = TRUE)), .default = NULL)
#> <environment: 0x55da2e2869d8>
# Equivalent to function(x) attr(x[[1]], "a")

as_mapper(c("a", "b", "c"), .default = NA)
#> function (x, ...) 
#> pluck_raw(x, list("a", "b", "c"), .default = NA)
#> <environment: 0x55da2e217df8>