par_lapply: Run a Task in Parallel

Description

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, ...)

Value

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

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.

Details

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

Examples

Run this code

# \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)

# 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)

# }

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