运行闪亮的应用程序时访问/使用 R 控制台

Question

Does anybody know if one is able to access the R console when running a shiny app? (running the shiny application in background would also be helpful, if that's possible)

I need this for manipulating objects in .GlobalEnv which are used in the shiny application and this has to be done using the command line.

When starting the app the console is buzy. Is there a possibility to access the console from within the application?

Thanks in advance!

Answer 1

R (and shiny) run single-threaded. This thread is used by the shiny application so you cannot interact with R whenever the app is running. If you want to run interactive commands during a shiny session you need to put a browser() inside your application like mentioned by @eric-canton.

A very simple application could look like this

library(shiny)

d <- data.frame(1:10, 1:10)

ui <-  fluidPage(
  actionButton("browser", "Trigger browser()"),
  actionButton("reload", "Reload Plot"),
  plotOutput("plot")
)


server <- function(input, output, session) {
  observeEvent(input$browser, {
    browser()
    1 + 1
  })

  output$plot <- renderPlot({
    input$reload
    plot(d)
  })
}

shinyApp(server = server, ui = ui)

Some comments about the code

• I put 1 + 1 after the browser() command because setting browser() as the last argument tends to stop the interactive terminal unexpectedly in my experience
• You need some shiny event to trigger the redrawing of the plot, because d is not a reactive value
• If you are on the console you need to assign a new value to d by using the <<- operator because d lives outside the function you are calling:

Browse[2]> d <<- data.frame(x = 1:200, y = 200:1)

• You can jump out of interactive console and resume the app by entering c and hitting Enter

Answer 2

Well, I had the similar doubt! In my case, the solution was to create my own Shiny server: https://github.com/rstudio/shiny-server

On the one hand, I have my app inside RStudio IDE when I want to change or to test new elements. Indeed this is the testing version. To run the application you execute runApp(dir), each time the port changes.

On the other hand, I have the stable version inside the Shiny server. This is a helpful way to connect from different devices and have a operative version while you are doing some changes. The application is running all of time, you have to configurate your port inside this file: /etc/shiny-server/shiny-server.conf.

If you need more information about Shiny server, consult this website: https://rstudio.github.io/shiny-server/latest/#configuration-settings

Answer 3

Can't you use the <<- global assignment operator? I'm not sure how complicated the variable you need to set is, but say you just need to change some variable t to 5.

We could make a textBoxInput that changes the input$new_t variable. Then have an observer:

observeEvent(input$new_t, t <<- input$new_t)

Then, when input$new_t changes, the global variable t changes.

Edit: Another option is to put a browser() in the object that accesses the variable you need to change, right before the variable is accessed.