as_mapper
Convert an object into a mapper function
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 character
as_mapper(.f, ..., .null, .default = NULL)
# S3 method for numeric
as_mapper(.f, ..., .null, .default = NULL)
# S3 method for list
as_mapper(.f, ..., .null, .default = NULL)
Arguments
- .f
A function, formula, or atomic vector.
If a function, it is used as is.
If a formula, e.g.
~ .x + 2, it is converted to a function. There are three ways to refer to the arguments:For a single argument function, use
.For a two argument function, use
.xand.yFor more arguments, use
..1,..2,..3etc
This syntax allows you to create very compact anonymous functions.
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. Within a list, wrap strings in
get-attr()to extract named attributes. If a component is not present, the value of.defaultwill be returned.- ...
Additional arguments passed on to methods.
- .default, .null
Optional additional argument for extractor functions (i.e. when
.fis character, integer, or list). Returned when value is absent (does not exist) or empty (has length 0)..nullis deprecated; please use.defaultinstead.
Examples
# NOT RUN {
as_mapper(~ . + 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"), .null = NA)
# }