R object to create a message progress bar in R. Similar to txtProgressBar but output the progress bar using message() instead of cat(), preferred in R packages.

msg_progress_bar.R

#' Message progress bar
#' 
#' @description 
#' A simple progress bar to use in R packages where messages are prefered to console output.
#' 
#' @field iter Total number of iterations
#' @field i Current iteration
#' @field width Width of the R console
#' @field width_bar Width of the progress bar
#' @field progress The number of character printed (continous)
#' @field progress_step Addition to progress per iteration
#' 
#' @examples
#' test_bar <- function(i = 10){
#'  bar <- msg_progress_bar(i)
#'  for(j in 1:i){
#'    bar$increment()
#'    Sys.sleep(4/i)
#'    }
#'  }
#'  test_bar(100)
#'   
#' @author Mans Magnusson (MansMeg @ github)
#'   
msg_progress_bar <- 
  setRefClass(
    Class = "msg_progress_bar", 
    fields = list(iter = "numeric",
                  i = "numeric",
                  progress = "numeric",
                  progress_step = "numeric",
                  width = "numeric",
                  width_bar = "numeric"),
    
    methods = list(
      initialize = function(iter){
        'Initialize a messagebar object'
        .self$width <- getOption("width")
        .self$iter <- iter
        .self$i <- 0
        .self$progress <- 0
        white_part <- paste(rep(" ", (.self$width - 11) %/% 4), collapse="")
        init_length <- .self$width - ((.self$width - 11) %/% 4) * 4 - 11
        white_init <- paste(rep(" ", init_length), collapse="")
        .self$width_bar <- .self$width - init_length - 2 + 0.1
        .self$progress_step <- .self$width_bar / .self$iter
        message(paste(white_init, "|", white_part, "25%", white_part, "50%", white_part, "75%", white_part, "|","\n", white_init, "|", sep=""), appendLF = FALSE)
      },
      
      increment = function(){
        'A messagebar object.'
        if(.self$i > .self$iter) return(invisible(NULL))
        new_progress <- .self$progress + .self$progress_step
        diff_in_char <- floor(new_progress) - floor(.self$progress)
        if(diff_in_char > 0) {
          message(paste(rep("=", diff_in_char),collapse=""), appendLF = FALSE)
        }
        
        .self$progress <- new_progress
        .self$i <- .self$i + 1
        if(.self$i == .self$iter) message("|\n", appendLF = FALSE)
        
      }
    )
  )