Impossible to access input from within R Shiny UI module? - r

Question

I want to have the choices in a radioButtons input depend on the selection of a prior input, and I would like to wrap both inputs up in a UI module. I know that passing the inputs of one module to another requires passing to the server first. But I can't seem to access an input within the same UI.
Here's what I have in a single app.r (things will eventually get repeated over several tabs, thus the desire for a module, but we're keeping it simple for now):
library(shiny)
# Sidebar selector UI module
sidebarSel_ui <- function(id){
ns <- NS(id)
# conditional choices for secondInput based on firstInput
input2Choices <- if (ns(input$firstInput == 1)) { # having trouble here
list(
"Choice A"=1,
"Choice B"=2
)
} else {
list(
"Choice C"=1,
"Choice D"=2
)
}
# inputs
tagList(
radioButtons(
inputId=ns("firstInput"),
label="Choose one:",
choices=list(
"Choice 1"=1,
"Choice 2"=2),
selected=1
),
radioButtons(
inputId=ns("secondInput"),
label="Choose another",
choices=input2Choices,
selected=1
)
)
}
# Define UI
ui <- fluidPage(
# Sidebar
sidebarLayout(
sidebarPanel(
sidebarSel_ui("test")
),
# Main panel
mainPanel(
)
)
)
# Define server
server <- function(input, output, session) {
}
# Run the application
shinyApp(ui = ui, server = server)
I'm getting an "object 'input' not found" error. If I do actually have to split these inputs into different modules, send the results of the first to the server and then send that back to the second to make it work, I think I can figure that out. It seems odd to not be able to access inputs within the same UI.

Answer 1

I figured it out thanks to the hint from #Limey:
library(shiny)
# Sidebar selector UI module
sidebarSel_ui <- function(id){
ns <- NS(id)
# inputs
tagList(
radioButtons(
inputId=ns("firstInput"),
label="Choose one:",
choices=list(
"Choice 1"=1,
"Choice 2"=2),
selected=1
),
radioButtons(
inputId=ns("secondInput"),
label="Choose another",
choices=list(
"Choice A"=1,
"Choice B"=2
),
selected=1
)
)
}
# Sidebar selector server module
sidebarSel_server <- function(id){
moduleServer(
id,
function(input, output, session){
observeEvent(input$firstInput,{
# conditional choices for input2 based on input1
input2Choices <- if (input$firstInput == 1) {
list(
"Choice A"=1,
"Choice B"=2
)
} else {
list(
"Choice C"=1,
"Choice D"=2
)
}
updateRadioButtons(session, "secondInput", choices=input2Choices)
})
})
}
# Define UI
ui <- fluidPage(
# Sidebar
sidebarLayout(
sidebarPanel(
sidebarSel_ui("test")
),
# Main panel
mainPanel(
)
)
)
# Define server
server <- function(input, output, session) {
sidebarSel_server("test")
}
# Run the application
shinyApp(ui = ui, server = server)
Key changes:
set up the second radioButtons input as usual with the first set of choices
set up an observeEvent in the module server that handles the if logic and
spits the choices list back with updateRadioButtons
call the module server in the main server function
More roundabout than I was expecting, and it looks like one cannot, in fact, refer to the inputs of a module ui within the module ui itself. The trick is to do the work in the module server and kick it back to the ui.