r - Shiny slider on logarithmic scale

Question

I'm using Shiny to build a simple web application with a slider that controls what p-values should be displayed in the output.

How can I make the slider act on a logarithmic, rather than linear, scale?

At the moment I have:

sliderInput("pvalue",
            "PValue:",
            min = 0,
            max = 1e-2,
            value = c(0, 1e-2)
),

Thanks!

Answer 1

I wasn't sure exactly what you wanted as the output, but what I did was have the possible p-values be [0, 0.00001, 0.0001, 0.001, 0.01]. If you want something a little different, hopefully this answer is a good enough starting point.

Basically, first I created an array that holds the values of the numbers (0, 0.0000.1, ...), and then I just use the special update function from the slider's API to make these values stick to the slider. It's pretty simple once you figure out how to use the slider's API. Also, for some reason running this inside RStudio looks weird, but in a browser it's fine. Also, note that I have a 5ms delay because I want to make sure this runs after the slider gets initialized. Not the cleanest solution, there's probably a better way to do that, but it works.

library(shiny)

JScode <-
  "$(function() {
    setTimeout(function(){
      var vals = [0];
      var powStart = 5;
      var powStop = 2;
      for (i = powStart; i >= powStop; i--) {
        var val = Math.pow(10, -i);
        val = parseFloat(val.toFixed(8));
        vals.push(val);
      }
      $('#pvalue').data('ionRangeSlider').update({'values':vals})
    }, 5)})"

runApp(shinyApp(
  ui = fluidPage(
    tags$head(tags$script(HTML(JScode))),

    sliderInput("pvalue",
                "PValue:",
                min = 0,
                max = 1e-2,
                value = c(0, 1e-2)
    )
  ),
  server = function(input, output, session) {
  }
))