R/future-map.R

In DavisVaughan/furrr: Apply Mapping Functions in Parallel using Futures

#' Apply a function to each element of a vector via futures
#'
#' These functions work exactly the same as [purrr::map()] and its variants, but
#' allow you to map in parallel.
#'
#' @inheritParams purrr::map
#'
#' @param .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`.
#'
#' @param .options The `future` specific options to use with the workers. This
#'   must be the result from a call to [furrr_options()].
#'
#' @param .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](https://CRAN.R-project.org/package=progressr)
#'   package.
#'
#' @return 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.
#'
#' @export
#' @examples
#' library(magrittr)
#' \donttest{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)
#' \donttest{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"))
#'
#' \dontshow{
#' # Close open connections for R CMD Check
#' if (!inherits(plan(), "sequential")) plan(sequential)
#' }
future_map <- function(.x,
                       .f,
                       ...,
                       .options = furrr_options(),
                       .env_globals = parent.frame(),
                       .progress = FALSE) {
  furrr_map_template(
    x = .x,
    fn = .f,
    dots = list(...),
    options = .options,
    progress = .progress,
    type = "list",
    map_fn = purrr::map,
    env_globals = .env_globals
  )
}

#' @rdname future_map
#' @export
future_map_chr <- function(.x,
                           .f,
                           ...,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  furrr_map_template(
    x = .x,
    fn = .f,
    dots = list(...),
    options = .options,
    progress = .progress,
    type = "character",
    map_fn = purrr::map_chr,
    env_globals = .env_globals
  )
}

#' @rdname future_map
#' @export
future_map_dbl <- function(.x,
                           .f,
                           ...,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  furrr_map_template(
    x = .x,
    fn = .f,
    dots = list(...),
    options = .options,
    progress = .progress,
    type = "double",
    map_fn = purrr::map_dbl,
    env_globals = .env_globals
  )
}

#' @rdname future_map
#' @export
future_map_int <- function(.x,
                           .f,
                           ...,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  furrr_map_template(
    x = .x,
    fn = .f,
    dots = list(...),
    options = .options,
    progress = .progress,
    type = "integer",
    map_fn = purrr::map_int,
    env_globals = .env_globals
  )
}

#' @rdname future_map
#' @export
future_map_lgl <- function(.x,
                           .f,
                           ...,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  furrr_map_template(
    x = .x,
    fn = .f,
    dots = list(...),
    options = .options,
    progress = .progress,
    type = "logical",
    map_fn = purrr::map_lgl,
    env_globals = .env_globals
  )
}

#' @rdname future_map
#' @export
future_map_raw <- function(.x,
                           .f,
                           ...,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  furrr_map_template(
    x = .x,
    fn = .f,
    dots = list(...),
    options = .options,
    progress = .progress,
    type = "raw",
    map_fn = purrr::map_raw,
    env_globals = .env_globals
  )
}

#' @rdname future_map
#' @export
future_map_dfr <- function(.x,
                           .f,
                           ...,
                           .id = NULL,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  if (!rlang::is_installed("dplyr")) {
    rlang::abort("`future_map_dfr()` requires dplyr")
  }

  res <- future_map(
    .x = .x,
    .f = .f,
    ...,
    .options = .options,
    .env_globals = .env_globals,
    .progress = .progress
  )

  dplyr::bind_rows(res, .id = .id)
}

#' @rdname future_map
#' @export
future_map_dfc <- function(.x,
                           .f,
                           ...,
                           .options = furrr_options(),
                           .env_globals = parent.frame(),
                           .progress = FALSE) {
  if (!rlang::is_installed("dplyr")) {
    rlang::abort("`future_map_dfc()` requires dplyr")
  }

  res <- future_map(
    .x = .x,
    .f = .f,
    ...,
    .options = .options,
    .env_globals = .env_globals,
    .progress = .progress
  )

  dplyr::bind_cols(res)
}

# ------------------------------------------------------------------------------

#' Apply a function to each element of a vector conditionally via futures
#'
#' These functions work exactly the same as [purrr::map_if()] and
#' [purrr::map_at()], but allow you to run them in parallel.
#'
#' @inheritParams purrr::map_if
#' @inheritParams future_map
#'
#' @return Both functions return a list the same length as `.x` with the
#' elements conditionally transformed.
#'
#' @export
#' @examples
#' \donttest{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)
#' \dontshow{
#' # Close open connections for R CMD Check
#' if (!inherits(plan(), "sequential")) plan(sequential)
#' }
future_map_if <- function(.x,
                          .p,
                          .f,
                          ...,
                          .else = NULL,
                          .options = furrr_options(),
                          .env_globals = parent.frame(),
                          .progress = FALSE) {
  sel <- probe(.x, .p)
  out <- purrr::list_along(.x)

  out[sel] <- future_map(
    .x = .x[sel],
    .f = .f,
    ...,
    .options = .options,
    .env_globals = .env_globals,
    .progress = .progress
  )

  if (is_null(.else)) {
    out[!sel] <- .x[!sel]
  } else {
    out[!sel] <- future_map(
      .x = .x[!sel],
      .f = .else,
      ...,
      .options = .options,
      .env_globals = .env_globals,
      .progress = FALSE
    )
  }

  set_names(out, names(.x))
}

#' @rdname future_map_if
#' @export
#' @inheritParams purrr::map_at
future_map_at <- function(.x,
                          .at,
                          .f,
                          ...,
                          .options = furrr_options(),
                          .env_globals = parent.frame(),
                          .progress = FALSE) {
  sel <- inv_which(.x, .at)
  out <- purrr::list_along(.x)

  out[sel] <- future_map(
    .x = .x[sel],
    .f = .f,
    ...,
    .options = .options,
    .env_globals = .env_globals,
    .progress = .progress
  )

  out[!sel] <- .x[!sel]

  set_names(out, names(.x))
}