How to render multiple output from the same analysis without executing it multiple time? (Shiny)

Question

I am writing an shiny app in which contains an stochastic function generates four objects - one plot and three tables. However, I want to render each object in different tabs without being executing the function four times since this stochastic function will generates four different versions. I have been researched online and find a lot people recommend "reactive()" but I still don't quite understand how to apply it to my problem. How can I use those four objects on rendering with only one execution on the function?

My "server.R" structure basically looks like the below:

shinyServer(function(input, output) {

     stochastic_function() {
          ...
       plot1 <- ...
       table1 <- ...
       table2 <- ...
       table3 <- ...
       result <- list(plot, table1, table2, table3)
     return(result)
     }

 output$plot <- renderPlot({

})

 output$table1 <- renderTable({

})

 output$table2 <- renderTable({

})

 output$table3 <- renderTable({

})

...

So, I have tried something like below for the stochastic function:

model <- eventReactive(input$goButton, {
        reactive(WG_Model(cdata = cdata(), # load data from outside env
                          sdata = sdata(), # load data from outside env
                          N = input$n, 
                          end_date = input$end_date,
                          cpx_goal = input$cpx,
                          N_new = input$n2, 
                          end_date_new = input$end_date2,
                          spend_range = input$s_range,
                          spend_incr = input$s_incr
                          ) 
                )
})

The idea is to add an "GoButton" to initiate the function and then save all outputs in a reactive fun(). So I can render each output with:

 output$plot <- renderPlot({
   model$gplot
})

 output$table <- renderTable({
   model$table
})

# Render UI section 
 output$tb <- renderUI({
  tabsetPanel(tabPanel("About Model", plotOutput("plot")), 
              tabPanel("About Model", tableOutput("table")))

  })

However, I only got "Error: object of type 'closure' is not subsettable" in the UI output. Which part did I miss?

Hey @warmoverflow :) I haven't tried anything yet but I am thinking using "model <- reactive(function() {..})" to store all outputs into a list. Then, render each output with list indexing like "render...(model()$plot)". I am trying it. — Mark Li
– Mark Li, Commented May 6, 2016 at 15:37
@warmoverflow I have tested it and got error message. I updated the post with the result. Please let me know if you have an idea. Thanks!:) — Mark Li
– Mark Li, Commented May 6, 2016 at 16:15
Within reactiveEvent you don't need anymore reactive. model should return a value which you can access with model(). You forgot to add brackets within your render* functions. (it should be model()$table) — Michal Majka
– Michal Majka, Commented May 6, 2016 at 16:23
@UnnamedUser is correct, you need to use model(), but also this won't get what you want, as I think every time you call model() it runs the code again. — Xiongbing Jin
– Xiongbing Jin, Commented May 6, 2016 at 16:57
@warmoverflow I see. I followed the solution provided by "@UnnamedUser". Though the function is successfully initiated and finished, I didn't get any plot or table on the UI. ;( — Mark Li
– Mark Li, Commented May 6, 2016 at 17:03

Michal Majka · Accepted Answer · 2016-05-06 17:48:53Z

4

If your model() is a list and contains data for all tables and a plot, it should work as in my example.

In this app, after pressing a button, a random number and data for a table and a plot are generated. Then the number, data for table and a plot are returned as a list and rendered with appropriate render* functions.

This app illustrates that the model function won't be re-run after accessing it with model() in other reactive functions.

However, there is an odd thing...the plot is not always rendered. You sometimes have to click the button few times to get the plot. The table is working always.

library(shiny)

ui <- shinyUI(fluidPage(
   br(),
   actionButton("numb", "generate a random numbers"),
   br(),
   br(),
   verbatimTextOutput("text"),
   plotOutput("plot"),
   tableOutput("table")
))

server <- shinyServer(function(input, output) {

  model <- eventReactive(input$numb, {
    # draw a random number and print it
    random <- sample(1:100, 1)
    print(paste0("The number is: ", random))

    # generate data for a table and plot
    data <- rnorm(10, mean = 100)
    table <- matrix(data, ncol = 2)

    # create a plot 
    Plot <- plot(1:length(data), data, pch = 16, xlab ="", ylab = "")

    # return all object as a list
    list(random = random, Plot = Plot, table = table)
  })

   output$text <- renderText({
     # print the random number after accessing "model" with brackets.
     # It doesn't re-run the function.
     youget <- paste0("After using model()$random you get: ", model()$random,
                      ". Compare it with a value in the console")
     print(youget)
     youget
   })

   output$plot <- renderPlot({
     # render saved plot
     model()$Plot
   })

   output$table <- renderTable({

     model()$table
   })
})


shinyApp(ui = ui, server = server)

answered May 6, 2016 at 17:48

Michal Majka

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9 Comments

Mark Li Over a year ago

No, it was just a small typo.;P Thanks! Oh by the way, a quick question just in case you know the answer - while running the model() function, it prints a lot of log information by using "print("xxx")" in console. Is there a way I can render those "Print()" log information to the UI?

Mark Li Over a year ago

Yes, this could be a way but I want to show user the log text while the model() is running. Since it is an optimization search function, I would like user to see what's happening while the model() is running. Is it possible?

Xiongbing Jin Over a year ago

It is not possible (or I am not aware of) any method that can output message to UI while a reactive process is running (output will appear after the reactive process ends). The root cause is that both Shiny and R are single-threaded, and it cannot do two tasks in the same time.

Mark Li Over a year ago

@UnnamedUser Thank you for sharing! This is very helpful! Why sometimes there is nothing happened after I hit "Go!" button and after a while it starts to run?

Mark Li Over a year ago

@warmoverflow Gotcha - Makes sense. Thanks for clarification!:)

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