Is it possible to stop executing of R code inside shiny (without stopping the shiny process)?

Question

Let\'s say I have a shiny app that has a function that can take a long time to run. Is it possible to have a \"stop\" button that tells R to stop the long-running call, wit

Answer 1

Provided you can split the heavy duty calculations into several parts, or have access to the part of the code that is involved in the computation, you can insert a breaker part. I implemented this in a Shiny app that listens for a button press before continuing with the rest of the calculation. You can run the app from R by

library(shiny)
runGitHub("romunov/shinyapps", subdir = "breaker")

or copy/paste the code into a server.R and ui.R and run it using runApp().

#ui.R
library(shiny)

shinyUI(fluidPage(

  titlePanel("Interrupting calculation"),

  sidebarLayout(
    sidebarPanel(
      sliderInput(inputId = "num.rows", 
                  label = "Generate number of rows",
                  min = 1e1,
                  max = 1e7,
                  value = 3e3),
      actionButton(inputId = "ok", label = "Stop computation")
    ),
    mainPanel(
      verbatimTextOutput("result")
    )
  )
))

#server.R
library(shiny)

shinyServer(function(input, output) {
  initial.ok <- 0

  part1 <- reactive({
    nr.f <- floor(input$num.rows/2)
    out1 <- data.frame(col = sample(letters[1:5], size = nr.f, 
                                    replace = TRUE), 
                       val = runif(nr.f))
    out1
  })

  part2 <- reactive({

    nr.c <- ceiling(input$num.rows/2)
    out2 <- data.frame(col = sample(letters[1:5], size = nr.c, 
                                    replace = TRUE),
                       val = runif(nr.c))
    out2
  })

  output$result <- renderPrint({

    out1 <- part1()

    if (initial.ok < input$ok) {
      initial.ok <<- initial.ok + 1
      stop("Interrupted")
    }

    out2 <- part2()
    out <- rbind(out1, out2)

    print("Successful calculation")
    print(str(out))
  })
})