Disable selectinput once user selected multiple choices in R shiny

Question

I have a selectinput with multiple = TRUE, I need to disable the selectinput once user select the multiple choices. But the selectinput is disabling once I select the first choice and it is not allowing me to select second choice. I have used following code.

library(shiny)
library(shinyjs)

ui <- fluidPage(
  br(),
  useShinyjs(),
  fluidRow(
    column(
      width = 6,
      selectInput(inputId = "check1", label = "Choose", choices = c("choice A","choice B","choice C"),multiple = T),
      verbatimTextOutput(outputId = "res1")
    )
  )
)
server <- function(input, output, session) {
  
  flag_lifecycle <- reactiveValues(val = "Yes")
  
  output$res1 <- renderPrint({
    input$check1
  })
  
  observeEvent(input$check1, {
    shinyjs::disable("check1")
  })
  
}
shinyApp(ui = ui, server = server)

The output I got

Here, selectinput should be disabled only when multiple choice has been selected.

Any help here is appreciated. Thanks in advance!

Answer 1

In the current setup you don't actually know when user has finished the selection.

Consider various scenarios -

• If you disable after 1st selection then user cannot select 2 or 3 values.
• If you disable after 2nd selection then user cannot select 3 values.
• If you disable after 3rd then what if user only want to select 1 value ?

You'll never know when to disable based on length of values. I think a better option would be to provide an actionButton for user to submit after they are done with their selection.

library(shiny)
library(shinyjs)

ui <- fluidPage(
  br(),
  useShinyjs(),
  fluidRow(
    column(
      width = 6,
      selectInput(inputId = "check1", label = "Choose", 
                  choices = c("choice A","choice B","choice C"), multiple = T),
      verbatimTextOutput(outputId = "res1"), 
      actionButton('submit', 'Done')
    )
  )
)
server <- function(input, output, session) {
  
  flag_lifecycle <- reactiveValues(val = "Yes")
  
  output$res1 <- renderPrint({
    input$check1
  })
  
  observeEvent(input$submit, {
    shinyjs::disable("check1")
  })
  
}
shinyApp(ui = ui, server = server)

Answer 2

Use selectizeInput() .

The function below adds 2 functionalities to your selectizeInput() :

• Ability to remove an already made choice.
• Limit max number of items that can be selected.

# ----selectizeInput options---
selectizeOptions <- function (n = NULL) { # n is the max number of items
  if (is.null(n)) {
    list(
      plugins = list("remove_button")
    )
  }else {
    list(
      plugins = list("remove_button"), 
      maxItems = n
    )
  }
}

Here is an example:

library(shiny)

ui <- fluidPage(
  # ----selections here----
  selectizeInput(
    inputId = "thechoices",
    label = "Choose",
    choices = LETTERS,
    selected = "A", 
    multiple = TRUE,
    options = selectizeOptions(n = 4)
  )
)

server <- function(input, output, session) {
  
}

shinyApp(ui, server)