Code from Intro to Shiny (2016 DSSC Hackathon Preparation Session)

server.R

library(shiny)

shinyServer(function(input, output) {
  
  data <- reactive({
    if(input$distribution_type == 1) {
      rnorm(n = 500, mean = input$parameter, sd = 1)
    } else {
      rpois(n = 500, lambda = input$parameter)
    }
  })
  
  output$sample_size <- renderPrint({
    if(input$distribution_type == 1) {
      print("This is a normal distribution\n")
    } else {
      print("This is a Poisson distribution\n")
    }
    print(range(data()))
  })
  
  output$plot <- renderPlot({
    p <- ggplot(mapping = aes(data())) + geom_histogram(fill = "blue") + xlim(c(-5, 20))
    if(input$title) {
      p + ggtitle("My Title Here")
    } else {
      p
    }
  })
  
})

ui.R

library(shiny)
library(ggplot2)

shinyUI(
  pageWithSidebar(
    headerPanel("My First Shiny App!"),
    sidebarPanel(
      h1("Sidebar"),
      sliderInput('parameter', 
                  'Parameter of Distribution',
                  min = 0.1,
                  max = 10,
                  step = 0.05,
                  value = 5),
      selectInput('distribution_type',
                  'Distribution Type',
                  c('Normal' = 1, 'Poisson' = 2)),
      checkboxInput('title', 'Include Title?')
      
    ),
    mainPanel(
      h1("Main Panel"),
      textOutput('sample_size'),
      plotOutput('plot')
    )
  )
)