vignettes/progressr-21-map-reduce.md

In progressr: An Inclusive, Unifying API for Progress Updates

Progress updates by progressr are designed to work out of the box for any iterator framework in R, e.g. lapply(), foreach, purrr, and plyr. Below you will find a set of examples that illustrate how to use progressr in common use cases.

Base R apply functions

library(progressr)
handlers(global = TRUE)

my_fcn <- function(xs) {
  p <- progressor(along = xs)
  lapply(xs, function(x) {
    Sys.sleep(0.1)
    p(sprintf("x=%g", x))
    sqrt(x)
  })
}

y <- my_fcn(1:10)
#  |====================                               |  40%

The foreach package

library(foreach)
library(progressr)
handlers(global = TRUE)

my_fcn <- function(xs) {
  p <- progressor(along = xs)
  foreach(x = xs) %do% {
    Sys.sleep(0.1)
    p(sprintf("x=%g", x))
    sqrt(x)
  }
}

y <- my_fcn(1:10)
#  |====================                               |  40%

The purrr package

library(purrr)
library(progressr)
handlers(global = TRUE)

my_fcn <- function(xs) {
  p <- progressor(along = xs)
  map(xs, function(x) {
    Sys.sleep(0.1)
    p(sprintf("x=%g", x))
    sqrt(x)
  })
}

y <- my_fcn(1:10)
#  |====================                               |  40%

The plyr package

library(plyr)
library(progressr)
handlers(global = TRUE)

my_fcn <- function(xs) {
  p <- progressor(along = xs)
  llply(xs, function(x, ...) {
    Sys.sleep(0.1)
    p(sprintf("x=%g", x))
    sqrt(x)
  })
}

y <- my_fcn(1:10)
#  |====================                               |  40%

Note how this solution does not make use of plyr's .progress argument, because the above solution is more powerful and more flexible, e.g. we have more control over progress updates and their messages. However, if you prefer the traditional plyr approach, you can use .progress = "progressr", e.g. y <- llply(..., .progress = "progressr").

progressr documentation built on March 31, 2026, 9:07 a.m.