Apply a Function to Multiple List or Vector Arguments

future_mapply() implements base::mapply() using futures with perfect replication of results, regardless of future backend used. Analogously to mapply(), future_mapply() is a multivariate version of future_sapply(). It applies FUN to the first elements of each \ldots argument, the second elements, the third elements, and so on. Arguments are recycled if necessary.

Usage

future_Map(
  f,
  ...,
  future.envir = parent.frame(),
  future.label = "future_Map-%d"
)

future_mapply(
  FUN,
  ...,
  MoreArgs = NULL,
  SIMPLIFY = TRUE,
  USE.NAMES = TRUE,
  future.envir = parent.frame(),
  future.stdout = TRUE,
  future.conditions = "condition",
  future.globals = TRUE,
  future.packages = NULL,
  future.seed = FALSE,
  future.scheduling = 1,
  future.chunk.size = NULL,
  future.label = "future_mapply-%d"
)

future_.mapply(FUN, dots, MoreArgs, ..., future.label = "future_.mapply-%d")

Arguments

f: A function of the arity \(k\) if future_Map() is called with \(k\) arguments.
future.envir: An environment passed as argument envir to future::future() as-is.
future.label: If a character string, then each future is assigned a label sprintf(future.label, chunk_idx). If TRUE, then the same as future.label = "future_lapply-%d". If FALSE, no labels are assigned.
FUN: A function to apply, found via base::match.fun().
MoreArgs: A list of other arguments to FUN.
SIMPLIFY: A logical or character string; attempt to reduce the result to a vector, matrix or higher dimensional array; see the simplify argument of base::sapply().
USE.NAMES: A logical; use names if the first \ldots argument has names, or if it is a character vector, use that character vector as the names.
future.stdout: If TRUE (default), then the standard output of the underlying futures is captured, and re-outputted as soon as possible. If FALSE, any output is silenced (by sinking it to the null device as it is outputted). If NA (not recommended), output is not intercepted.
future.conditions: A character string of conditions classes to be captured and relayed. The default is the same as the condition argument of future::Future(). To not intercept conditions, use conditions = character(0L). Errors are always relayed.
future.globals: A logical, a character vector, or a named list for controlling how globals are handled. For details, see future_lapply().
future.packages: (optional) a character vector specifying packages to be attached in the R environment evaluating the future.
future.seed: A logical or an integer (of length one or seven), or a list of max(lengths(list(...))) with pre-generated random seeds. For details, see future_lapply().
future.scheduling: Average number of futures ("chunks") per worker. If 0.0, then a single future is used to process all elements of X. If 1.0 or TRUE, then one future per worker is used. If 2.0, then each worker will process two futures (if there are enough elements in X). If Inf or FALSE, then one future per element of X is used. Only used if future.chunk.size is NULL.
future.chunk.size: The average number of elements per future ("chunk"). If Inf, then all elements are processed in a single future. If NULL, then argument future.scheduling is used.
dots: A list of arguments to vectorize over (vectors or lists of strictly positive length, or all of zero length).
...: Arguments to vectorize over, will be recycled to common length, or zero if one of them is of length zero.

Value

future_Map() is a simple wrapper to future_mapply() which does not attempt to simplify the result. See base::Map() for details.

future_mapply() returns a list, or for SIMPLIFY = TRUE, a vector, array or list. See base::mapply() for details.

future_.mapply() returns a list. See base::.mapply() for details.

Details

Note that base::.mapply(), which future_.mapply() is modeled after is listed as an "internal" function in R despite being exported.

Author

The implementations of future_Map() is adopted from the source code of the corresponding base R function Map(), which is licensed under GPL (>= 2) with 'The R Core Team' as the copyright holder.

Examples

## ---------------------------------------------------------
## mapply()
## ---------------------------------------------------------
y0 <- mapply(rep, 1:4, 4:1)
y1 <- future_mapply(rep, 1:4, 4:1)
stopifnot(identical(y1, y0))

y0 <- mapply(rep, times = 1:4, x = 4:1)
y1 <- future_mapply(rep, times = 1:4, x = 4:1)
stopifnot(identical(y1, y0))

y0 <- mapply(rep, times = 1:4, MoreArgs = list(x = 42))
y1 <- future_mapply(rep, times = 1:4, MoreArgs = list(x = 42))
stopifnot(identical(y1, y0))

y0 <- mapply(function(x, y) seq_len(x) + y,
             c(a =  1, b = 2, c = 3),  # names from first
             c(A = 10, B = 0, C = -10))
y1 <- future_mapply(function(x, y) seq_len(x) + y,
                    c(a =  1, b = 2, c = 3),  # names from first
                    c(A = 10, B = 0, C = -10))
stopifnot(identical(y1, y0))

word <- function(C, k) paste(rep.int(C, k), collapse = "")
y0 <- mapply(word, LETTERS[1:6], 6:1, SIMPLIFY = FALSE)
y1 <- future_mapply(word, LETTERS[1:6], 6:1, SIMPLIFY = FALSE)
stopifnot(identical(y1, y0))


## ---------------------------------------------------------
## Parallel Random Number Generation
## ---------------------------------------------------------
# \donttest{
## Regardless of the future plan, the number of workers, and
## where they are, the random numbers produced are identical

plan(multisession)
set.seed(0xBEEF)
y1 <- future_mapply(stats::runif, n = 1:4, max = 2:5,
                    MoreArgs = list(min = 1), future.seed = TRUE)
print(y1)
#> [[1]]
#> [1] 1.094084
#> 
#> [[2]]
#> [1] 1.133518 1.415726
#> 
#> [[3]]
#> [1] 3.992017 3.395174 3.470525
#> 
#> [[4]]
#> [1] 2.693828 1.588631 2.708467 4.411477
#> 

plan(sequential)
set.seed(0xBEEF)
y2 <- future_mapply(stats::runif, n = 1:4, max = 2:5,
                    MoreArgs = list(min = 1), future.seed = TRUE)
print(y2)
#> [[1]]
#> [1] 1.094084
#> 
#> [[2]]
#> [1] 1.133518 1.415726
#> 
#> [[3]]
#> [1] 3.992017 3.395174 3.470525
#> 
#> [[4]]
#> [1] 2.693828 1.588631 2.708467 4.411477
#> 

stopifnot(all.equal(y1, y2))
# }