how to call a shiny module in another shiny module (reactive function from one module to the other)

Question

I'd like to know how to access reactive functions in one module to another module. If I have more than one reactive function in a module can I access them each in another module?

So basically how would I call/pass a reactive function in one shiny module to another shiny module (reactive function from one module to the other) Thanks

module1Ui <- function(id) {
  ns <- NS(id)

  wellPanel(selectInput(
    ns("cars"),
    "cars:",
    list(
      "Select" = "",
      "a" = "mazda",
      "b" = "ford"
    )
  ))
}


module1 <- function(input, output, session) {
  dataone <- reactive({
    if (input$cars == "mazda") {
      mtcars$mpg
    }
    else {
      (mtcars$hp)
    }
  })
}
module2 <- function(input, output, session) {
  dataone()
  # here I want dataone from the above module1
  # I tried to use callmodule(module1,_) but then didnt understand what the id would be in this case?
}

library(shiny)

ui <-
  fluidPage(
    sliderInput("slider", "how much cars?", 1, 10, 1, width = "100%"),
    uiOutput("selectors"),
    verbatimTextOutput("datap")
  )

server <- function(input, output, session) {
  for (i in 1:10)
    callModule(module1, i)
  output$selectors <- renderUI({
    lapply(1:input$slider, module1Ui)
  })

  # below  code just to test if I was able to correctly get dataone()      #from module2
  output$datap <- renderPrint(lapply(1:input$slider, function(i) {
    datas <- callModule(module2, i)
    datas()
  }))
}

shinyApp(ui, server)

Thanks

Answer 1

You need to use return in the module to return the reactive to the app or the module which calls your nested module. In the calling layer, use <- to assign the returned value. Then it is usable in the layer that calls your nested module. See the working example:

module1Ui <- function(id) {
  ns <- NS(id)

  wellPanel(selectInput(ns("cars"), "Select", c("mpg", "hp")))
}


module1 <- function(input, output, session) {
  dataone <- reactive({
    req(!is.null(input$cars))
    return(input$cars)
  })

  # return dataone so that it is visible in the app
  return(dataone)
}
module2 <- function(input, output, session, dataone) {
  # if you want to use dataone() here, you need to do so in a reactive context, e.g. observe, render*, ...
  observeEvent(dataone(), {
    print(dataone())
  })

  # return dataone so that it is visible in the app
  return(dataone)
}

library(shiny)

ui <-
  fluidPage(
    sliderInput("slider", "how much cars?", 1, 10, 1, width = "100%"),
    uiOutput("selectors"),
    verbatimTextOutput("datap")
  )

server <- function(input, output, session) {
  # create a list for all dataone-Vectors
  dataones <- list()
  for (i in 1:10)
    # fill the list with each dataone
    dataones[[i]] <- callModule(module1, i)

  output$selectors <- renderUI({
    lapply(1:input$slider, module1Ui)
  })

  # below  code just to test if I was able to correctly get dataone()
  #from module2
  output$datap <- renderPrint({
    lapply(1:input$slider, function(i) {
      datas <- callModule(module2, i, dataones[[i]])
      return(paste("Input", i, "returned", datas()))
    })
  })
}

shinyApp(ui, server)