Add server.R

function(input, output) {

  regFormula <- reactive({

    as.formula(paste('mpg ~', input$x))

  })

  output$regPlot <- renderPlot({

    par(mar = c(4, 4, .1, .1))

    plot(regFormula(), data = mtcars, pch = 19)

  })

  output$downloadReport <- downloadHandler(

    filename = function() {

      paste('my-report', sep = '.', switch(

        input$format, PDF = 'pdf', HTML = 'html', Word = 'docx'

      ))

    },

    content = function(file) {

      src <- normalizePath('report.Rmd')

      # temporarily switch to the temp dir, in case you do not have write

      # permission to the current working directory

      owd <- setwd(tempdir())

      on.exit(setwd(owd))

      file.copy(src, 'report.Rmd', overwrite = TRUE)

      library(rmarkdown)

      out <- render('report.Rmd', switch(

        input$format,

        PDF = pdf_document(), HTML = html_document(), Word = word_document()

      ))

      file.rename(out, file)

    }

  )

}

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