SelectInput基于R Shiny中先前的SelectInput更新值

Question

The R shiny script below creates three selectInputs such that the values of each selectInput depend upon the input value of the previous selectInput. Eg in the data in the script, "value" column values depend on "Candy" column and "Candy" column values depend on the "Brand". The issue is that, whether I select "Mars" or "Netle" value in the "Brand" column, The corresponding "Candy" value "100Grand" is same for both, hence I do not see a change in the value column as the selectInput is reading the same value. Kindly help me to fix this, also please ensure the script does not become slow. Thanks.

candyData <- read.table(
text = "
Brand       Candy           value
Mars        100Grand        Choc1
Netle       100Grand        Choc2
Nestle      Crunch          Choc3",
header = TRUE,
stringsAsFactors = FALSE)
library(shiny)
library(shinydashboard)
submenuUI <- function(id) {
ns <- NS(id)
tagList(
box(title = "Data", status = "primary", solidHeader = T, width = 12,
    fluidPage(
      fluidRow(

        column(2,offset = 0, style='padding:1px;',

selectInput(ns("Select1"),"select1",unique(candyData$Brand))),
        column(2,offset = 0,

style='padding:1px;',selectInput(ns("Select2"),"select2",choices = NULL)),
        column(2, offset = 0,

style='padding:1px;',selectInput(ns("Select3"),"select3",choices=NULL ))
      )))
)
}
submenuServ <- function(input, output, session){
observeEvent(input$Select1,{
updateSelectInput(session,'Select2',
choices=unique(candyData$Candy[candyData$Brand==input$Select1]))
})
observeEvent(input$Select2,{
updateSelectInput(session,'Select3',
choices=unique(candyData$value[candyData$Brand==input$Select1 &
candyData$Candy==input$Select2]))
})
}
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(
sidebarMenu(
  shinyjs::useShinyjs(),
  id = "tabs",
  menuItem("Charts", icon = icon("bar-chart-o"),
           shinyjs::hidden(menuSubItem("dummy", tabName = "dummy")),
           menuSubItem("Sub-item 1", tabName = "subitem1")
  ))),
dashboardBody(
tabItems(tabItem("dummy"),
         tabItem("subitem1", submenuUI('submenu1'))
)
))
server <- function(input, output,session) {
callModule(submenuServ,"submenu1")
}
shinyApp(ui = ui, server = server)

Answer 1

You can just add input$Select1 in your observeEvent to update select3

submenuServ <- function(input, output, session){
    observeEvent(input$Select1,{
        updateSelectInput(session,'Select2',
                          choices=unique(candyData$Candy[candyData$Brand==input$Select1]))
    })
    observeEvent(c(input$Select1, input$Select2),{
        updateSelectInput(session,'Select3',
                          choices=unique(candyData$value[candyData$Brand==input$Select1 &
                                                             candyData$Candy==input$Select2]))
    })
}

If you want, you can convert the observeEvent to observe :

observe({
    updateSelectInput(
        session, 'Select3',
        choices= unique(candyData$value[candyData$Brand==input$Select1 & candyData$Candy==input$Select2])
    )
})