future_map_if {furrr}

Apply a function to each element of a vector conditionally via futures

Description

These functions work exactly the same as purrr::map_if() and purrr::map_at(), but allow you to run them in parallel.

Usage

future_map_if(
  .x,
  .p,
  .f,
  ...,
  .else = NULL,
  .options = furrr_options(),
  .env_globals = parent.frame(),
  .progress = FALSE
)

future_map_at(
  .x,
  .at,
  .f,
  ...,
  .options = furrr_options(),
  .env_globals = parent.frame(),
  .progress = FALSE
)

Arguments

.x

A list or atomic vector.

.p

A single predicate function, a formula describing such a predicate function, or a logical vector of the same length as .x. Alternatively, if the elements of .x are themselves lists of objects, a string indicating the name of a logical element in the inner lists. Only those elements where .p evaluates to TRUE will be modified.

.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.

.else

A function applied to elements of .x for which .p returns FALSE.

.options

The future specific options to use with the workers. This must be the result from a call to furrr_options().

.env_globals

The environment to look for globals required by .x and .... Globals required by .f are looked up in the function environment of .f.

.progress

A single logical. Should a progress bar be displayed? Only works with multisession, multicore, and multiprocess futures. Note that if a multicore/multisession future falls back to sequential, then a progress bar will not be displayed.

Warning: The .progress argument will be deprecated and removed in a future version of furrr in favor of using the more robust progressr package.

.at

A character vector of names, positive numeric vector of positions to include, or a negative numeric vector of positions to exlude. Only those elements corresponding to .at will be modified. If the tidyselect package is installed, you can use vars() and the tidyselect helpers to select elements.

Value

Both functions return a list the same length as .x with the elements conditionally transformed.

Examples

plan(multisession, workers = 2)

# Modify the even elements
future_map_if(1:5, ~.x %% 2 == 0L, ~ -1)

future_map_at(1:5, c(1, 5), ~ -1)