Second histogram example, with density estimate

server.r

shinyServer(function(input, output) {

  output$main_plot <- renderPlot(width = 400, height = 300, {

    hist(faithful$eruptions,
      probability = TRUE,
      breaks = as.numeric(input$n_breaks),
      xlab = "Duration (minutes)",
      main = "Geyser eruption duration")

    if (input$individual_obs) {
      rug(faithful$eruptions)
    }

    if (input$density) {
      dens <- density(faithful$eruptions, adjust = input$bw_adjust)
      lines(dens, col = "blue")
    }

  })
})

ui.r

shinyUI(bootstrapPage(

  selectInput(inputId = "n_breaks",
              label = "Number of bins in histogram (approximate):",
              choices = c(10, 20, 35, 50),
              selected = 20),

  checkboxInput(inputId = "individual_obs",
                label = strong("Show individual observations"),
                value = FALSE),

  checkboxInput(inputId = "density",
                label = strong("Show density estimate"),
                value = FALSE),

  plotOutput(outputId = "main_plot", height = "300px"),

  # Display this only if the density is shown
  conditionalPanel(condition = "input.density == true",
    sliderInput(inputId = "bw_adjust",
                label = "Bandwidth adjustment:",
                min = 0.2, max = 2, value = 1, step = 0.2)
  )

))