Custom progress bars for RcppProgress

December 27, 2017

[This article was first published on Rcpp Gallery, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

is a tool to help you monitor the execution time of your C++ code, by
providing a way to interrupt the execution inside the C++ code, and also to
display a progress bar indicative of the state of your computation. Additionally,
it is compatible with multi-threaded code, for example using OpenMP.
The initial (yet updated) article explains the
basic setup.

Since version 0.4 it became more simple to create custom progress bars. In this new
article we will show how to do this. Our final example displays a progress bar which
provides an estimation of the remaining time (ETA) to finish a computation.

A minimal example

Imagine you added a progress bar with RcppProgress to your function
long_computation() following the example from the first article mentioned above.

// [[Rcpp::depends(RcppProgress)]]
// [[Rcpp::export]]
double long_computation(int nb, bool display_progress=true) {
    double sum = 0;
    Progress p(nb*nb, display_progress);
    for (int i = 0; i < nb; ++i) {
        if (Progress::check_abort() )
            return -1.0;
        for (int j = 0; j < nb; ++j) {
            sum += R::dlnorm(i+j, 0.0, 1.0, 0);
    return sum + nb;
[1] 12.20382

What you get is a basic and useful console visualization that looks like this:

0%   10   20   30   40   50   60   70   80   90   100%

That’s the default, platform independent display in RcppProgress defined in
It’s OK for most purposes to give you an idea how much work is done and it also allows
you to make a very intuitive estimation about how long it’s going to take to finish.
But of course that’s not everything a progress bar could show you. A progress bar
could give you information about the running progress or about performance parameters
of your system. It could contain calculated estimates of passed and remaining time.
After all it could just look much more fancy to impress your colleagues.

RcppProgress makes it now easy to create your own implementation of a progress bar class.
Your own class has to be derived from the abstract class ProgressBar that defines some
basic virtual methods:

class ProgressBar {
    virtual ~ProgressBar() = 0;
    virtual void display() = 0;
    virtual void update(float progress) = 0;
    virtual void end_display() = 0;

display() starts the display that will be updated by subsequent calls of
update(). end_display finalizes it. Your progress bar implementation should
not rely on the destructor to finalize the display.

A very minimal setup could look something like this:


// [[Rcpp::depends(RcppProgress)]]
#include "progress_bar.hpp"

class MinimalProgressBar: public ProgressBar{
    MinimalProgressBar()  {
        _finalized = false;
    ~MinimalProgressBar() {}
    void display() {
      REprintf("Progress: ");
    void update(float progress) {
      if (_finalized) return;
    void end_display() {
      if (_finalized) return;
      _finalized = true;
    bool _finalized;

// [[Rcpp::export]]
double long_computation_minimal(int nb, bool display_progress=true) {
    MinimalProgressBar pb;
    double sum = 0;
    Progress p(nb, display_progress, pb);
    for (int i = 0; i < nb; ++i) {
        if (Progress::check_abort() )
            return -1.0;
        for (int j = 0; j < nb; ++j) {
            sum += R::dlnorm(i+j, 0.0, 1.0, 0);
    return sum + nb;
[1] 12.20382

The display() method in this example does nothing more than printing the word
Progress. update() concatenates a + symbol every time Progress::increment() is
called. The result looks like this:

Progress: ++++++++++

In comparison to the example of the default progress bar above, I moved the
call to increment() out of the second level and into the first level loop to keep
the amount of console output at bay. update() also checks if the display is _finalized.
end_display triggers the finalization.

Remaining time estimation

Based on the minimal setup above, you can implement more sophisticated
progress bars. Here’s an example of one that looks exactly like the default
SimpleProgressBar, but adds an estimation of the remaining time for the process to finish.
You can find a complete package setup with the code for this ETAProgressBar
In this article we only highlight some crucial aspects of the implementation.

We use the Rinterface.h header to update the display dynamically. Unfortunately this header is only available for Unix-like systems.
A less cool, old version of an ETA progress bar that also works on windows can be
found here.
The following preprocessor statements load Rinterface.h if the code is compiled
on a non-windows computer.

#if !defined(WIN32) && !defined(__WIN32) && !defined(__WIN32__)

The class ETAProgressBar inherits from the abstract class ProgressBar.
It has an integer variable _max_ticks that controls the amount of individual
tick symbols necessary to reach the 100% mark of the progress bar. That depends
on the display you want to craft. ETAProgressBar also has a boolean flag variable
_timer_flag that acts as a switch to separate the initial starting turn where
the time measurement starts and the following turns where the time is picked off.
The measured time values are stored in two variables start and end of class
time_t (from ctime).

class ETAProgressBar: public ProgressBar{

  // ...
    int _max_ticks;
    bool _finalized;
    bool _timer_flag;
    time_t start,end;
  // ...  

The display() function initializes the progress bar visualization. The first two lines
are hard coded ASCII art.

void display() {
  REprintf("0%%   10   20   30   40   50   60   70   80   90   100%%\n");

update() is the most important function for the progress bar mechanism. The if clause
allows to separate the initial call of update() from the following ones to start the time
counter. Afterwards the time passed is calculated and transformed to a human readable string
by the custom function _time_to_string(). _current_ticks_display() is another custom
function to transform the progress information to a string with the correct amount of *
symbols and filling whitespaces. The progress string and the time string are concatenated
to create the additional third line below the initial two lines drawn by display().
A string with sufficient whitespaces is also added to ensure that this dynamically updated
line is overwritten completely from turn to turn. REprintf("\r"); triggers a carriage return
to make this continuous overwriting possible.

void update(float progress) {
    // stop if already finalized
    if (_finalized) return;
    // start time measurement when update() is called the first time
    if (_timer_flag) {
        _timer_flag = false;
        // measure start time
    } else {
        // measure current time
        // calculate passed time and remaining time (in seconds)
        double pas_time = std::difftime(end, start);
        double rem_time = (pas_time / progress) * (1 - progress);
        // convert seconds to time string
        std::string time_string = _time_to_string(rem_time);
        // create progress bar string 
        std::string progress_bar_string = _current_ticks_display(progress);
        // ensure overwriting of old time info
        int empty_length = time_string.length();
        std::string empty_space = std::string(empty_length, ' ');
        // merge progress bar and time string
        std::stringstream strs;
        strs << "|" << progress_bar_string << "| " << time_string << empty_space;
        std::string temp_str = strs.str();
        char const* char_type = temp_str.c_str();
        // print: remove old display and replace with new
        REprintf("%s", char_type);
        // finalize display when ready
        if(progress == 1) {

_time_to_string() parses time information given in form of a floating point number of
seconds to a human-readable string. The basic algorithm is based on an example from

std::string _time_to_string(double seconds) {
    int time = (int) seconds;
    int hour = 0;
    int min = 0;
    int sec = 0;
    hour = time / 3600;
    time = time % 3600;
    min = time / 60;
    time = time % 60;
    sec = time;
    std::stringstream time_strs;
    if (hour != 0) time_strs << hour << "h ";
    if (min != 0) time_strs << min << "min ";
    if (sec != 0) time_strs << sec << "s ";
    std::string time_str = time_strs.str();
    return time_str;

_current_ticks_display() relies on _compute_nb_ticks() to first of all transform
the progress information (floating point number between 0 and 1) to a natural number
that expresses the correct fraction of _max_ticks. _construct_ticks_display_string()
takes this value and parses a string with * symbols and whitespaces that can be plotted
as a visual progress indication.

std::string _current_ticks_display(float progress) {
    int nb_ticks = _compute_nb_ticks(progress);
    std::string cur_display = _construct_ticks_display_string(nb_ticks);
    return cur_display;

int _compute_nb_ticks(float progress) {
    return int(progress * _max_ticks);

std::string _construct_ticks_display_string(int nb) {
    std::stringstream ticks_strs;
    for (int i = 0; i < (_max_ticks - 1); ++i) {
        if (i < nb) {
            ticks_strs << "*";
        } else {
            ticks_strs << " ";
    std::string tick_space_string = ticks_strs.str();
    return tick_space_string;

flush_console() is a wrapper around R_FlushConsole() which is called to flush any
pending output to the system console. It’s necessary to do this when the display is started
in display() and when it’s closed in _finalize_display().

void flush_console() {
#if !defined(WIN32) && !defined(__WIN32) && !defined(__WIN32__)

The output of an ETAProgressBar looks like this:

0%   10   20   30   40   50   60   70   80   90   100%
|*******                                          | 49s

To leave a comment for the author, please follow the link and comment on their blog: Rcpp Gallery. offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

If you got this far, why not subscribe for updates from the site? Choose your flavor: e-mail, twitter, RSS, or facebook...

Comments are closed.

Search R-bloggers


Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)