Run a Task in Parallel

This function can be used to run a task in parallel. The task is executed in parallel on the specified backend, similar to parallel::parLapply(). If backend = NULL, the task is executed sequentially using base::lapply(). See the Details section for more information on how this function works.

Usage

par_lapply(backend = NULL, x, fun, ...)

Arguments

backend

An object of class Backend as returned by the start_backend() function. It can also be NULL to run the task sequentially via base::lapply(). The default value is NULL.

x

An atomic vector or list to pass to the fun function.

fun

A function to apply to each element of x.

...

Additional arguments to pass to the fun function.

Value

A list of the same length as x containing the results of the fun. The output format resembles that of base::lapply().

Details

This function uses the UserApiConsumer class that acts like an interface for the developer API of the parabar package.

See also

start_backend(), peek(), export(), evaluate(), clear(), configure_bar(), par_sapply(), par_apply(), stop_backend(), set_option(), get_option(), Options, UserApiConsumer, and BackendService.

Examples

# \donttest{

# Define a simple task.
task <- function(x) {
    # Perform computations.
    Sys.sleep(0.01)

    # Return the result.
    return(x + 1)
}

# Start an asynchronous backend.
backend <- start_backend(cores = 2, cluster_type = "psock", backend_type = "async")

# Run a task in parallel.
results <- par_lapply(backend, x = 1:300, fun = task)

# Disable progress tracking.
set_option("progress_track", FALSE)

# Run a task in parallel.
results <- par_lapply(backend, x = 1:300, fun = task)

# Enable progress tracking.
set_option("progress_track", TRUE)

# Change the progress bar options.
configure_bar(type = "modern", format = "[:bar] :percent")

# Run a task in parallel.
results <- par_lapply(backend, x = 1:300, fun = task)

# Stop the backend.
stop_backend(backend)

# Start a synchronous backend.
backend <- start_backend(cores = 2, cluster_type = "psock", backend_type = "sync")

# Run a task in parallel.
results <- par_lapply(backend, x = 1:300, fun = task)
#> Warning: Progress tracking not supported for backend of type 'SyncBackend'.

# Disable progress tracking to remove the warning that progress is not supported.
set_option("progress_track", FALSE)

# Run a task in parallel.
results <- par_lapply(backend, x = 1:300, fun = task)

# Stop the backend.
stop_backend(backend)

# Run the task using the `base::lapply` (i.e., non-parallel).
results <- par_lapply(NULL, x = 1:300, fun = task)

# }