How to format R Shiny numericInput?

The shinyWidgets package has a great new function (added as of version 0.5.4, also a disclaimer, I added it via a pull request), autonumericInput that will allow you to do just this. It is based on the javascript library autonumeric. There are a lot of options to the function, but the documentation is extensive and for simple uses most can be ignored.

What you are trying to do can be accomplished as follows:

library(shiny)
library(shinyWidgets)

ui <- fluidPage(
  h1("Autonumeric Input Example"),
  shinyWidgets::autonumericInput(
    inputId = "num", 
    label = "Enter a large number:", 
    value = 1000000, 
    currencySymbolPlacement = "p",
    decimalPlaces = 2,
    digitGroupSeparator = ",",
    decimalCharacter = "."
  ),
  verbatimTextOutput("res1")
)

server <- function(input, output) {
  output$res1 <- renderText(input$num)
}

shinyApp(ui = ui, server = server)

This is especially nice because it provides as-you-type formatting, so that the user can easily know how big the number is as they put it in. I know from experience that it is a real pain to try to put large numbers into the base shiny numericInput, trying to count digits in a small little box and figure out how many zeros there are. The goal of this function is to make formatting numeric inputs much easier.

Hopefully this is useful!