shiny-modules

library(shiny)

# You can put input to both your functions
mod_ui <- function(id, title){
  # The ns here is a function that will help to 'namespace' the ids
  # In other words, it will turn "go" into "chosennamespace-go"
  ns <- NS(id)
  tagList(
    h2(title),
    selectInput(
      # with mod_ui("ui1"), it will create an id 'ui1-what'
      # with mod_ui("ui2"), it will create an id 'ui2-what'
      # So that way I'm sure what happens in ui1 is caught by the 
      # correct server function
      ns("what"), 
      "What", 
      choices = c("iris", "mtcars", "airquality")
    ), 
    plotOutput(ns("plot"))
  )
}

# You can put input to both your function
mod_server <- function(input, output, session){
  # I dont' need ns() here, the callModule makes sure 
  # to par the good ui-namespace with the good server call
  output$plot <- renderPlot({
    switch(
      input$what, 
      "iris" = plot(iris), 
      "mtcars" = plot(mtcars), 
      "airquality" = plot(airquality)
    )
  })
  # Your module can return a value if you want
}

ui <- fluidPage(
  column(6, mod_ui("ui1", title = "left")),
  column(6, mod_ui("ui2", title = "right"))
)

server <- function(input, output, session) {
  # I use the module server function + the ui id it refers to
  # When shiny is run, the mod_ui("ui1") is watched by the first 
  # callModule, "ui2" by the second one
  callModule(mod_server, "ui1")
  callModule(mod_server, "ui2")
}

shinyApp(ui, server)