Modularized shiny app using conditional panels (modified from the shiny::conditionalPanel help page)

conditionalPanel_usage_in_module.R

# The following code is based on the shiny::conditionalPanel() help page. The `ui` and `server`
# components have been compartmentalized into the `mod_histogram` module. The `histogramApp`
# function shows an example of using this module.
# Note that the `ns = ns` argument needs to be passed ot the conditionalPanel() call.

library(shiny)

mod_histogram_ui <- function(id){
    ns <- NS(id)
    fluidPage(
      sidebarPanel(
        selectInput(ns("plotType"), "Plot Type",
                    c(Scatter = "scatter", Histogram = "hist")
        ),
        # Only show this panel if the plot type is a histogram
        conditionalPanel(
          condition = "input.plotType == 'hist'",
          ns = ns,
          selectInput(
            ns("breaks"), "Breaks",
            c("Sturges", "Scott", "Freedman-Diaconis", "[Custom]" = "custom")
          ),
          # Only show this panel if Custom is selected
          conditionalPanel(
            condition = "input.breaks == 'custom'",
            ns = ns,
            sliderInput(ns("breakCount"), "Break Count", min = 1,
                        max = 100, value = 10)
          )
        )
      ),
      mainPanel(
        plotOutput(ns("plot"))
      )
    )
}

mod_histogram_server <- function(id, df, labels, interactive = FALSE){
  moduleServer( id, function(input, output, session){
    x <- rnorm(1000)
    y <- rnorm(1000)

    output$plot <- renderPlot({
      if (input$plotType == "scatter") {
        plot(x, y)
      } else {
        breaks <- input$breaks
        if (breaks == "custom") {
          breaks <- input$breakCount
        }
        hist(x, breaks = breaks)
      }
    })
  })
}

histogramApp <- function() {
  ui <- mod_histogram_ui("histogram_1")
  server <- function(input, output, session) {
    mod_histogram_server("histogram_1")
  }

  shinyApp(ui, server)
}