app.R

shinyApp(
  ui = fluidPage(
    sidebarPanel(
      sliderInput("slider", "Slider", 1, 100, 50),
      downloadButton("report", "Generate report")),
    mainPanel(
      plotOutput("distPlot", height = "650px"))
  ),
  
  server = function(input, output) {
    library(ggplot2)
    
    output$distPlot <- renderPlot({
      # generate bins based on input$bins from ui input
      p <- ggplot(faithful, aes(x=waiting)) + geom_histogram(bins = input$slider) + theme_bw()
      print(p)
    })
    
    output$report <- downloadHandler(
      # For PDF output, change this to "report.pdf"
      filename = "report.html",
      content = function(file) {
        # Copy the report file to a temporary directory before processing it, in
        # case we don't have write permissions to the current working dir (which
        # can happen when deployed).
        tempReport <- file.path(tempdir(), "report.Rmd")
        file.copy("report.Rmd", tempReport, overwrite = TRUE)
        
        # Set up parameters to pass to Rmd document
        params <- list(n = input$slider)
        
        # Knit the document, passing in the `params` list, and eval it in a
        # child of the global environment (this isolates the code in the document
        # from the code in this app).
        rmarkdown::render(tempReport, output_file = file, 
                          params = params,
                          envir = new.env(parent = globalenv())
        )
      }
    )
  }
)