Constructing URL search parameters in Shiny app?

Question

I have a Shiny app that wrangles a large csv file. Currently the user can select a facility_id number from a drop down menu to get a specific plot, see https://r.timetochange.today/shiny/Annual_Emissions2/. I would like to pass this id with a URL parameter like /?selected_facilities=1010040 so I can embed the plots in another website.

I have taken the code from How do you pass parameters to a shiny app via URL and tried to use it to update my selectInput() value in the server section of the Shiny app, but I don't really understand how the UI part is constructed so I am not getting it right. Any help would really be appreciated! Here is the relevant code:

#### shiny UI ####
facilities <- unique(ghg_emissions$facility_id)

ui <- fluidPage(
  titlePanel("Annual Greenhouse Gas Emissions"),
  sidebarLayout(
    sidebarPanel(
      selectInput("selected_facility", 
                  "Select facility", 
                  choices = facilities) # select input gives the drop down menu to select facilities
    ),
    mainPanel(
      plotlyOutput("facility_plot")
    )
  )
)

#### shiny server ####
server <- function(input, output, session) {
  # Here you read the URL parameter from session$clientData$url_search
  observe({
    query <- parseQueryString(session$clientData$url_search)
    if (!is.null(query[['selected_facility']])) {
      updateSelectInput(session, "selected_facility", value = query[['selected_facility']])
    }
  })

Answer 1

Your UI is good, the issue with the updateSelectInput, use selected rather than value and include choices.

Minimal working example:

library(shiny)

facilities <- seq(1:5)

ui <- fluidPage(
    
    selectInput("selected_facility", "Select facility", choices = facilities)
    
)

server <- function(input, output, session) {
    
    observe({
       
        #Get URL query
        query <- parseQueryString(session$clientData$url_search)
        
        #Ignore if the URL query is null
        if (!is.null(query[['selected_facility']])) {

            #Update the select input
            updateSelectInput(session, "selected_facility", selected  = query[['selected_facility']], choices = facilities)
            
        }
        
    })
    
}

shinyApp(ui, server)

To test, run your shiny app, click 'Open in Browser' and append your query to the URL, e.g.

127.0.0.1:6054/?selected_facility=4