R: Convert an object into a mapper function

as_mapper {purrr} | R Documentation

## 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 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.
`.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(~ . + 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)

[Package purrr version 0.2.4 Index]