Dynamically populate a grouped list of choices in SelectInput (RShiny)

Question

I would like to create a selectInput with options based on a data frame I load. These options should be grouped, as in the example below. I know how to do it when writing out in full, however, I want the dropdown list be be automated so it changes automatically when I change the data frame. I might change the list of groups, or the list of indicators withinin each group.

DD <- data.frame(group=c("Diagnosis","Diagnosis", "Treatment", "Treatment", "Outcome", "Outcome", "Outcome"),
                 Indicator=LETTERS[1:7])


> DD
      group Indicator
1 Diagnosis         A
2 Diagnosis         B
3 Treatment         C
4 Treatment         D
5   Outcome         E
6   Outcome         F
7   Outcome         G

This is the style I am after:

runApp(
  list(
    ui = fluidPage(
      sidebarLayout(
        sidebarPanel(
          selectInput(inputId  = "IND", 
                      label    = "Select indicator:", 
                      choices  =  list("Diagnosis" = c("A", "B"),
                                       "Treatment" = c("C", "D"),
                                       "Outcome" = c("E", "F", "G")))
          , width = 3),

        mainPanel(
          )
        )
      )


    , server = function(input, output, session){
    }
  )
)

Answer 1

One option would be to be split the 'Indicator' by 'group' column

library(shiny)
DD <- data.frame(group=c("Diagnosis","Diagnosis", "Treatment", 
      "Treatment", "Outcome", "Outcome", "Outcome"),
             Indicator=LETTERS[1:7])
runApp(
  list(
    ui = fluidPage(
      sidebarLayout(
        sidebarPanel(
          selectInput(inputId  = "IND", 
                      label    = "Select indicator:", 
                      choice = split(DD$Indicator, DD$group))
          , width = 3),

        mainPanel(
        )
      )
    )


    , server = function(input, output, session){
    }
  )
)

-output