Execute script after Shiny App inputs have been entered

Question

I am relatively new to Shiny and am trying to create an app that creates a global variable that I can then pass to an R script. Here is an example of my Shiny App:

library(shiny)
 
ui <- fluidPage(
  titlePanel("Hello"),
  br(),
  h3("Welcome"),
  
  sidebarLayout(
    
    sidebarPanel(
      h1("Enter parameter value"),
      selectInput("datamodel", "Update Data Model",
                  choices = c("Yes", "No"),
                  selected = "No")
    ),
    
    mainPanel(
      h1("Output")
      
    )
  ))

# Define server logic
server <- function(input, output) {
  
  observe({
    Update_Data_Model <<- input$datamodel
  })  
  
  source("Authentication.R")
  
}


# Run the application shinyApp(ui = ui, server = server)

The UI is created and I am able to create a global variable called Update_Data_Model to pass to my R script called Authentication.R, however the R script runs before I have time to enter the input variable in the UI.

Is there a way to execute the R script once the input variables have been entered in the UI?

Ash · Accepted Answer · 2020-03-16 02:27:10Z

1

You can use observeEvent on the input itself, so it will only execute when that input changes:

library(shiny)

ui <- fluidPage(
  titlePanel("Hello"),
  br(),
  h3("Welcome"),

  sidebarLayout(

    sidebarPanel(
      h1("Enter parameter value"),
      selectInput("datamodel", "Update Data Model",
                  choices = c("Yes", "No"),
                  selected = "No")
    ),

    mainPanel(
      h1("Output")

    )
  ))

# Define server logic
server <- function(input, output) {

    observeEvent(input$datamodel, {

        Update_Data_Model <<- input$datamodel

        if(input$datamodel == 'Yes') {

            source("Authentication.R")

        }

    })

}

shinyApp(ui = ui, server = server)

Consider using an action button rather than a dropdown, it could be a bit more intuitive for you and your users:

library(shiny)

ui <- fluidPage(

    actionButton("mybutton", "Update Data Model")

)

server <- function(input, output) {

    observeEvent(input$mybutton, {

        source("Authentication.R")

    })

}

shinyApp(ui = ui, server = server)

edited Mar 16, 2020 at 2:27

answered Mar 16, 2020 at 0:52

Ash

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2 Comments

SteveM Over a year ago

Thanks. How would I go about using an action button? Could you provide an example like you did above for the use of observe event?

Ash Over a year ago

@SteveM I've updated the answer above to include one using an action button.

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