Displaying a Progress Bar in R/Shiny

Progress Bar in R

When running time-consuming loops in R, you can show progress to the user using the built-in functions txtProgressBar() and setTxtProgressBar(). Here’s how:

total <- 100
pb <- txtProgressBar(min = 0, max = total, style = 3)  # initialize
for (i in 1:total) {
  setTxtProgressBar(pb, i)  # Update progress
  Sys.sleep(0.1)  # Simulate a time-consuming task
}
close(pb)  # Close

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Progress Bar in Shiny

You can create a dynamic progress bar in R Shiny by rendering a custom UI component that updates as your process runs. Here is a minimal example.

Place this UI output in your ui definition where you want the progress bar to appear:

ui <- fluidPage(
  uiOutput("progressUI"),
  # ... other UI components ...
)

In your server function, use renderUI() to dynamically update the progress bar:

output$progressUI <- renderUI({
  progress <- progressVal()   # progressVal() should return a value between 0 and 1
  if (progress > 0 && progress < 1) {
    progressPercent <- progress * 100
    tags$div(class = "progress",
             tags$div(class = "progress-bar progress-bar-striped progress-bar-animated",
                      role = "progressbar",
                      style = sprintf("width: %s%%;", progressPercent),
                      sprintf("%.0f%%", progressPercent)))
  }
})

Use a reactive or observer in your server to update progressVal().

progressVal <- reactiveVal(0)
observe({
  for (i in 1:100) {
    Sys.sleep(0.05)
    progressVal(i / 100)
  }
})

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