purrr (version 0.3.4)

imap: Apply a function to each element of a vector, and its index

Description

imap_xxx(x, ...), an indexed map, is short hand for map2(x, names(x), ...) if x has names, or map2(x, seq_along(x), ...) if it does not. This is useful if you need to compute on both the value and the position of an element.

Usage

imap(.x, .f, ...)
imap_lgl(.x, .f, ...)
imap_chr(.x, .f, ...)
imap_int(.x, .f, ...)
imap_dbl(.x, .f, ...)
imap_raw(.x, .f, ...)
imap_dfr(.x, .f, ..., .id = NULL)
imap_dfc(.x, .f, ...)
iwalk(.x, .f, ...)

Value

A vector the same length as .x.

Arguments

.x

A list or atomic vector.

.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. 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. If a component is not present, the value of .default will be returned.

...

Additional arguments passed on to the mapped function.

.id

Either a string or NULL. If a string, the output will contain a variable with that name, storing either the name (if .x is named) or the index (if .x is unnamed) of the input. If NULL, the default, no variable will be created.

Only applies to _dfr variant.

See Also

Other map variants: invoke(), lmap(), map2(), map_if(), map(), modify()

Examples

# Note that when using the formula shortcut, the first argument
# is the value, and the second is the position
imap_chr(sample(10), ~ paste0(.y, ": ", .x))
iwalk(mtcars, ~ cat(.y, ": ", median(.x), "\n", sep = ""))