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().
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)
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 .x and .y
For more arguments, use ..1, ..2, ..3 etc
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
.default will be returned.
Additional arguments passed on to methods.
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.
# 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)
# }
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