Shiny won't render my chart unless I resize the window

Hi everyone,

Word of warning. I am a complete noob when it comes to Shiny!

I'm currently trying to translate some code I've written into a Shiny app and am having some problems. I've set the app up so that you upload a file (mp3), this is then analysed in some way and chart should display that analysis at the end.

I have it working in a very basic fashion but for some reason it will only render the plot if I resize the Shiny app window?!

Any thoughts or help would be most appreciated.

# Define UI for data upload app ----
ui <- fluidPage(
    # App title ----
    titlePanel("Uploading Files"),
    # Sidebar layout with input and output definitions ----
        # Sidebar panel for inputs ----
            # Input: Select a file ----
            fileInput("file1", "Choose MP3 File",
                      multiple = TRUE,
                      accept = c("audio/mp3",
            # Horizontal line ----
        # Main panel for displaying outputs ----
            # Output: Data file ----

# Define server logic to read selected file ----
server <- function(input, output) {
    output$plot <- renderPlot({
        # input$file1 will be NULL initially. After the user selects
        # and uploads a file, head of that data file by default,
        # or all rows if selected, will be shown.
        # load in the model
        model <<- load_model_hdf5("models/bob_cnn_dropout.h5")

        # get the album in the right order
        bands <<- c("band 1", "band 2")
        whom <<- predict_band(input$file1$datapath)
        track_name <- input$file1$name

        whom %>% 
            ggplot(aes(pos, is_track, colour = winner)) +
            geom_line() +
            theme(legend.position = "none") +
            scale_colour_gradient(low = "deeppink2", high = "grey35") +
            labs(title = track_name)


Feel free to mock the terrible code, it's all very hacky to get it to work.

Thanks, Chris

Here's a very basic app that does work:


ui <- fluidPage(
  fileInput("file1", "Upload"),

server <- function(input, output) {
  df <- reactive({
    data.frame(x = 1, y = 1, name = input$file1$name)
  output$plot <- renderPlot({
    df() %>%
      ggplot(aes(x, y)) + 
      geom_text(aes(label = name))
shinyApp(ui, server)

Things that I'd think about for your app:

  • It's probably unrelated, but I think you app will be easier to understand if you move the data frame generation into its own reactive.

  • You don't have an input control called "go" but you're referencing it.

  • The use of <<- is suspicious; I don't think you need it, and you don't need to be creating those objects every time that the input file changes (since they don't depend on the input you're just doing a lot of repeated work)

If that doesn't help, you'll need to create a more realistic reprex that other people can run on their computer.

Hi @hadley
Thanks very much for your help here and apologies for the pretty terrible reprex. As I said I was trying to circumvent actually learning Shiny and just shoving some bits in the hope I could put a front end on a presentation for a conference. My thoughts being maybe it's an option I've been unable to find and would be a simple "add x to your code".

In the future I'll be sure to actually learn the tool before leaping into it (and then complaining when I can't get it to work).

The input$go was left over from an old iteration I hadn't commented out and the <<- was more because I wanted to see what was coming out of things after the fact. But yes all very crappy.

Thanks again.

Oh and yes it worked, thank you.

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