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

These functions work 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, specified in one of the following ways:

A named function, e.g. mean.
An anonymous function, e.g. \(x) x + 1 or function(x) x + 1.
A formula, e.g. ~ .x + 1. Use .x to refer to the first argument. No longer recommended.
A string, integer, or list, e.g. "idx", 1, or list("idx", 1) which are shorthand for \(x) pluck(x, "idx"), \(x) pluck(x, 1), and \(x) pluck(x, "idx", 1) respectively. Optionally supply .default to set a default value if the indexed element is NULL or does not exist.

...

Additional arguments passed on to the mapped function.

We now generally recommend against using ... to pass additional (constant) arguments to .f. Instead use a shorthand anonymous function:

# Instead of
x |> future_map(f, 1, 2, collapse = ",")
# do:
x |> future_map(\(x) f(x, 1, 2, collapse = ","))

This makes it easier to understand which arguments belong to which function and will tend to yield better error messages.

.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 logical, integer, or character vector giving the elements to select. Alternatively, a function that takes a vector of names, and returns a logical, integer, or character vector of elements to select.

: if the tidyselect package is installed, you can use vars() and 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)
#> [[1]]
#> [1] 1
#> 
#> [[2]]
#> [1] -1
#> 
#> [[3]]
#> [1] 3
#> 
#> [[4]]
#> [1] -1
#> 
#> [[5]]
#> [1] 5
#> 

future_map_at(1:5, c(1, 5), ~ -1)
#> [[1]]
#> [1] -1
#> 
#> [[2]]
#> [1] 2
#> 
#> [[3]]
#> [1] 3
#> 
#> [[4]]
#> [1] 4
#> 
#> [[5]]
#> [1] -1
#>