Why does this reactive value needs to be called first before it can be used?

Question

While trying to come up with an overly complicated solution for this question, I stumbled across the following problem. I have 2 different modules, inputtable displays an rhandsontable and returns this table, and resulttable takes this table as the input, performs some calculation and displays the result as an rhandsontable. inputtable returns the rhandsontable object as a reactive value. Because there can be several copies of each module, I store the results from inputtable in a list and feed the list elements as the input to resulttable.

I've noticed that in resulttable, the reactive input input_data$input_table() can't directly be used. When I call a browser or print function or assign it to a variable before I use the reactive value for the actual purpose, then it works. Otherwise I get the error

attempt to apply non-function

As far as I understood passing reactive values to modules, this should work without the need to do something else to the reactive value before using it. If I don't use a list to store the reactive value, but only using one copy of each module and directly storing the result of inputtable in a variable and passing this to resulttable, it works as I would expect. (But storing the different reactive values in a reactiveValues object also leads to the error.)

Does someone know what is going on there?

I apologise for the long example, when I tried to shorten it I lost the error:

library(shiny)
library(rhandsontable)

# define the first module
resulttableUI <- function(id) {
  ns <- NS(id)
  tabPanel(title = ns(id),
           column(12,
                  rHandsontableOutput(ns("results_table"))))
}

resulttable <- function(id, input_data) {
  moduleServer(
    id,
    function(input, output, session) {
      # THE NEXT LINE NEEDS TO BE UNCOMMENTED TO MAKE IT WORK
      # used_data <- input_data$input_table()
      output$results_table <- renderRHandsontable({
        rhandsontable(hot_to_r(input_data$input_table())[2:5]/hot_to_r(input_data$input_table())[1:4])
      })
    }
  )
}

# define the second module
inputtableUI <- function(id) {
  ns <- NS(id)
  tabPanel(title = ns(id),
           column(12,
                  rHandsontableOutput(ns("input_table"))))
}

inputtable <- function(id, i) {
  moduleServer(
    id,
    function(input, output, session) {
      output$input_table <- renderRHandsontable({
        mat <- matrix(c(1:25) * i, ncol = 5, nrow = 5)
        mat <- as.data.frame(mat)
        rhandsontable(mat)
      })
      
      return(list(
        input_table = reactive({input$input_table})
      ))
    }
  )
}

ui <- navbarPage("App",
                 
                 tabPanel("Input",
                          numericInput('num_of_table', "Number of sub tabs: ", value = 1, min = 1, max = 10),
                          tabsetPanel(id = "insert_input")),
                 tabPanel("Results",
                          tabsetPanel(id = "insert_results"))
                 
)

number_modules <- 0
current_id <- 1

server <- function(input, output, session) {
  
  # variable to store the inputs from the modules
  input_data <- list()
  
  observeEvent(input$num_of_table, {
      modules_to_add <- input$num_of_table - number_modules
      for (i in seq_len(modules_to_add)) {
        # add the logic for the input
        input_data[[paste0("inputtable_", current_id)]] <<-
          inputtable(paste0("inputtable_", current_id), current_id)
        # add the logic for the results
        resulttable(paste0("resulttable_", current_id),
                    input_data = input_data[[paste0("inputtable_", current_id)]])
        
        # add the UI
        appendTab(inputId = "insert_input",
                  tab = inputtableUI(paste0("inputtable_", current_id)))
        appendTab(inputId = "insert_results",
                  tab = resulttableUI(paste0("resulttable_", current_id)))
        # update the id
        current_id <<- current_id + 1
        
      }
      
      number_modules <<- input$num_of_table
    
    updateTabsetPanel(session,
                      "insert_input",
                      "inputtable_1-inputtable_1")

  })
}


shinyApp(ui,server)

I'm using R 3.6.1 and shiny 1.5.0.

Unfortunately, there are 2 other issues:

You need to click on the result tab to render it
The first shown table from the inputtable module uses i = 2 instead of i = 1, I haven't figured out yet why.

So maybe there is something else wrong with my code. I'm glad for any hints for this strange behaviour or how to make a more minimal example.

Why does this reactive value needs to be called first before it can be used?

Answers (1)

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