server.R

library(ggplot2)

shinyServer(function(input, output, session) {

  data <- reactive({
    if (is.null(input$file))
      return(NULL)
    else if (identical(input$format, 'CSV'))
      return(read.csv(input$file$datapath))
    else
      return(read.delim(input$file$datapath))
  })
 
  observe({
    df <- data()
    str(names(df))
    if (!is.null(df)) {
      updateSelectInput(session, 'x', choices = names(df))
      updateSelectInput(session, 'y', choices = names(df))
      updateSelectInput(session, 'color', choices = c('None', names(df)))
      updateSelectInput(session, 'facet_row', choices = c(None='.', names(df)))
      updateSelectInput(session, 'facet_col', choices = c(None='.', names(df)))
    }
  })
 
  output$plot <- renderPlot({

    if (is.null(data()))
      return(NULL)
    
    p <- ggplot(data(), aes_string(x=input$x, y=input$y)) + geom_point()
    
    if (input$smooth)
      p <- p + geom_smooth()

    if (input$color != 'None')
      p <- p + aes_string(color=input$color)
    
    facets <- paste(input$facet_row, '~', input$facet_col)
    if (facets != '. ~ .')
      p <- p + facet_grid(facets)
    
    if (input$jitter)
      p <- p + geom_jitter()
    
    print(p)
    
  }, height=700)
  
})