14

I'm new to Shiny and struggling considerably.

I need to give my Shiny users the ability to download a data file (essentially querying a database). The query goes from one time to another. Shiny supports dates natively, but not time so I have to give the users a text field with a submitButton

The problem is I need to have the submit button do a validation test on both text inputs, and the either: 1) Return an error message if either input is not valid 2) Download the data, while giving status updates (data can take an hour easily--I do not want to leave users hanging).

I discovered something called renderPrint that seemed like a good option, in that it purports to output what has print to the console--then I can either print an error message or display the normal console output from the data download process. But then it holds the printed output until the whole process is done.

I'm thinking another possible solution would be to go back to renderText and then render text directly from the queryMagic function--as it goes through the data download process, it can periodically update output$text with new text. But I'm not sure how exactly to do this.

ui.R:

shinyUI(fluidPage(

  # Application title
  titlePanel("Demo Market Report"),

  fluidRow(

    column(4,
           h3("Extract Data"),
           helpText("Enter a start and end date/time of data to download. Be aware it takes about 10 minutes to download one hour of data.", strong("Date/time should be entered in yyyy-mm-dd hh:mm:ss format.")),
           textInput("fromDatetime", "From:", value = paste(with_tz(Sys.time(), "EST")-3600 )),
           textInput("toDatetime", "To:", value = paste(with_tz(Sys.time(), "EST"))),
           submitButton("Download Data Extract")
    ),
    column(4,
           textOutput("text1")
    )
  )


))

server.R:

shinyServer(
  function(input, output) {

    logText <- reactive({
      if (input$fromDatetime == "a") {
        data = queryMagic(blah,blah,blah) #this just gets the data, function is already used in production, I'll feed the shiny input into it but that seems straightforward
        return("victory")
      }
      else return("invalid")
    })

    output$text1 <- renderPrint({
      paste(logText())
    })


  }
)

Thanks in advance for help.

Michael Sherman
  • 523
  • 2
  • 5
  • 16

1 Answers1

4

I think capture.output is good solution for capturing text from console. 

 server <- function(input, output) {
  values <- reactiveValues()

  queryMagic <- function() {
    print("Warning")

    return("Data")
  }
  output$console <- renderPrint({
    logText()
    return(print(values[["log"]]))
    # You could also use grep("Warning", values[["log"]]) to get warning messages and use shinyBS package
    # to create alert message
  })

  logText <- reactive({
    values[["log"]] <- capture.output(data <- queryMagic())


  })
}

ui <- shinyUI(fluidPage(
  sidebarLayout(
    sidebarPanel(
    ),
    mainPanel(verbatimTextOutput("console"))
  )
))

shinyApp(ui = ui, server = server)
Mikael Jumppanen
  • 2,436
  • 1
  • 17
  • 29
  • Thanks (again) for help @Mikael . I'm off for holidays for the next 4 days, but I'll try this on Monday and write about how it goes. – Michael Sherman Nov 26 '14 at 22:01
  • 2
    Hi @Mikael . It seems this still holds all the output from queryMagic() until queryMagic finishes. Once queryMagic finishes all of the printed output then comes in the UI. ` queryMagic <- function() { print("Warning1") Sys.sleep(3) print("Warning2") Sys.sleep(3) print("Warning3") return("Data") }` – Michael Sherman Dec 01 '14 at 17:11
  • My immediate needs are solved by shiny's progress bar, but the core question is still unanswered – Michael Sherman Dec 01 '14 at 21:22
  • Edited question to improve title – Michael Sherman Dec 01 '14 at 21:22
  • Sorry, I down-voted. The suggested solution does not work and thus does not answer the question. I have the same problem and am looking for a solution. – Johannes Titz Mar 16 '20 at 14:14
  • A working solution can be found here: https://stackoverflow.com/questions/30474538/possible-to-show-console-messages-written-with-message-in-a-shiny-ui – Johannes Titz Mar 17 '20 at 09:13