future_map {furrr}

Apply a function to each element of a vector via futures

Description

These functions work exactly the same as purrr::map() and its variants, but allow you to map in parallel.

Usage

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

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

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

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

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

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

future_map_dfr(
  .x,
  .f,
  ...,
  .id = NULL,
  .options = furrr_options(),
  .env_globals = parent.frame(),
  .progress = FALSE
)

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

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

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.

.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.

.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.

Value

All functions return a vector the same length as .x.

• future_map() returns a list

• future_map_lgl() a logical vector

• future_map_int() an integer vector

• future_map_dbl() a double vector

• future_map_chr() a character vector

The output of .f will be automatically typed upwards, e.g. logical -> integer -> double -> character.

Examples

library(magrittr)
plan(multisession, workers = 2)

1:10 %>%
  future_map(rnorm, n = 10, .options = furrr_options(seed = 123)) %>%
  future_map_dbl(mean)

# If each element of the output is a data frame, use
# `future_map_dfr()` to row-bind them together:
mtcars %>%
  split(.$cyl) %>%
  future_map(~ lm(mpg ~ wt, data = .x)) %>%
  future_map_dfr(~ as.data.frame(t(as.matrix(coef(.)))))


# You can be explicit about what gets exported to the workers.
# To see this, use multisession (not multicore as the forked workers
# still have access to this environment)
plan(multisession)
x <- 1
y <- 2

# This will fail, y is not exported (no black magic occurs)
try(future_map(1, ~y, .options = furrr_options(globals = "x")))

# y is exported
future_map(1, ~y, .options = furrr_options(globals = "y"))