Apply R expressions in a parallel way

Usage

async_expr(
  .X,
  .expr,
  .varname = "x",
  envir = parent.frame(),
  .pre_run = NULL,
  .ncore = future::availableCores(),
  ...
)

Arguments

.X: a vector or a list to apply evaluation on
.expr: R expression, unquoted
.varname: variable name representing element of each .X
envir: environment to evaluate expressions
.pre_run: expressions to be evaluated before looping.
.ncore: number of CPU cores
...: passed to future::future

Value

a list whose length equals to .X. The value of each item returned depends on whether async is called. See details for workflow.

Details

async_expr uses lapply and future::future internally. Within each loop, an item in ".X" will be assigned to variable "x" (defined by ".varname") and enter the evaluation. During the evaluation, function async is provided. Expressions within async will be evaluated in another session, otherwise will be evaluated in current session. Below is the workflow:

Run .pre_run
For i in seq_along(.X):
- 1. Assign x with .X[[i]], variable name x is defined by .varname
- 2. Evaluate expr in current session.
  - a. If async is not called, return evaluated expr
  - b. If async(aync_expr) is called, evaluate aync_expr in another session, and return the evaluation results if aync_expr