Is there a way to display charts when they are building in Shiny, rather than waiting for them all?

Question

I have a Shiny Dashboard with many graphs, all of which take a few seconds to build. As soon as the latter builds, they are all displayed. I would like each chart to be displayed as soon as it ends. I understand that R is single-threaded, but it seems that there should be a way to “return execution to display code” or something like that.

This code demonstrates the problem:

library(shiny)

ui <- fluidPage(
  title = "Page loading test"
  , h1("Page loading test")
  , plotOutput("plot1")
  , plotOutput("plot2")
  , plotOutput("plot3")
  , plotOutput("plot4")
)

server <- function(input, output) {
   output$plot1 <- renderPlot({
     Sys.sleep(10)
     plot(rnorm(50))
   })

   output$plot2 <- renderPlot({
     Sys.sleep(10)
     plot(rnorm(50))
   })

   output$plot3 <- renderPlot({
     Sys.sleep(10)
     plot(rnorm(50))
   })

   output$plot4 <- renderPlot({
     Sys.sleep(10)
     plot(rnorm(50))
   })
}

shinyApp(ui = ui, server = server)

Dreams are simply emulating slow execution.

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Answer 1

reactiveTimer() .

list , .

renderPlot, step

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library(shiny)

ui <- fluidPage( 
  title = "Page loading test"
  , h1("Page loading test")
  , plotOutput("plot1")
  , plotOutput("plot2")
  , plotOutput("plot3")
  , plotOutput("plot4")
)

# Loading plot
plot(-1:1, -1:1, type = "n", xlab = "", ylab = "")
text(0,0, "Loading",cex = 5)
loading <- recordPlot()

plotlist <- vector("list",4) 
step <- 0 # which plot should be rendered next

server <- function(input, output, session) {
  autoInvalidate <- reactiveTimer(10, session)
  output$plot4 <- renderPlot({autoInvalidate();
    if(step>4){plotlist[[4]]}
    else if(step==4){step <<- step+1
    print("rendering step 4")
    Sys.sleep(10)
    plotlist[[4]] <<- {plot(rnorm(50));recordPlot()}} else loading
  })
  output$plot3 <- renderPlot({autoInvalidate();
    if(step>3){plotlist[[3]]}
    else if(step==3){step <<- step+1
    print("rendering step 3")
    Sys.sleep(10)
    plotlist[[3]] <<- {plot(rnorm(50));recordPlot()}} else loading
  })
  output$plot2 <- renderPlot({autoInvalidate();
    if(step>2){plotlist[[2]]}
    else if(step==2){step <<- step+1
    print("rendering step 2")
    Sys.sleep(10)
    plotlist[[2]] <<- {plot(rnorm(50));recordPlot()}} else loading
  })
  output$plot1 <- renderPlot({autoInvalidate();
    if(step>1){plotlist[[1]]}
    else if(step==1){step <<- step+1
    print("rendering step 1")
    Sys.sleep(10)
    plotlist[[1]] <<- {plot(rnorm(50));recordPlot()}} else {step <<-1;loading}
  })
}
shinyApp(ui = ui, server = server)