基于R shiny中常见服务器功能下的前一个selectInput更新selectInput

Question

在下面的R闪亮脚本中，我试图使功能在第一个子菜单中，每个selectInput值取决于前一列中的项目选择。附加数据并编写代码。但是我无法达到预期的效果。请运行代码并检查，我希望整个服务器逻辑只能在一个函数下运行。谢谢，请帮助。

library(shiny)
library(shinydashboard)
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(
sidebarMenu(

  id = "tabs",
  menuItem("Charts", icon = icon("bar-chart-o"),
           menuSubItem("Sub-item 1", tabName = "subitem1"),
           menuSubItem("Sub-item 2", tabName = "subitem2")
  ))),
dashboardBody(
tabItems(tabItem("subitem1", uiOutput("brand_selector")),
         tabItem("subitem2", 4))
))
server <- shinyServer(function(input, output) {
candyData <- read.table(
text = "
Brand       Candy           value
Nestle      100Grand        Choc1
Netle       Butterfinger    Choc2
Nestle      Crunch          Choc2
Hershey's   KitKat          Choc4
Hershey's   Reeses          Choc3
Hershey's   Mounds          Choc2
Mars        Snickers        Choc5
Nestle      100Grand        Choc3
Nestle      Crunch          Choc4
Hershey's   KitKat          Choc5
Hershey's   Reeses          Choc2
Hershey's   Mounds          Choc1
Mars        Twix            Choc3
Mars        Vaid            Choc2",
header = TRUE,
stringsAsFactors = FALSE)
output$brand_selector <- renderUI({
box(title = "Data", status = "primary", solidHeader = T, width = 12,
    fluidPage(
      fluidRow(
        Brand_Select <- unique(candyData$Brand),
        column(2,offset = 0, style='padding:1px;', 
selectInput("Select1","select1",Brand_Select)),
        Candy_Select <- candyData$Candy[candyData$Brand == input$Select1],
        Candy_Select <- unique(Candy_Select),
        column(2,offset = 0, style='padding:1px;', 
selectInput("Select2","select2",Candy_Select)),
        Value_Select <- candyData$value[candyData$Candy == input$Select2],
column(2, offset = 0, 
style='padding:1px;',selectInput("select3","select3",Value_Select ))
)))
})
})
shinyApp(ui = ui, server = server)

Answer 1

您的代码不起作用，因为每当其中一个输入发生变化时，整个renderUI会再次运行，从而重置所有输入，因为它们都是从头开始创建的！

那么我们如何解决这个问题呢？您可以尝试以下内容。请注意，我删除了许多不必要的格式，因此更容易看出它是如何工作的。

我们在UI中创建输入，并添加一些监听第一个或第二个输入中的更改的observeEvents。如果第一个输入发生更改，则会触发第一个observeEvent，并会更改input$Select2的选项。随后，这将触发第二个observeEvent，从而限制input$Select3中的选择。

我希望这有帮助！

library(shiny)
library(shinydashboard)

candyData <- read.table(
  text = "
    Brand       Candy           value
    Nestle      100Grand        Choc1
    Netle       Butterfinger    Choc2
    Nestle      Crunch          Choc2
    Hershey's   KitKat          Choc4
    Hershey's   Reeses          Choc3
    Hershey's   Mounds          Choc2
    Mars        Snickers        Choc5
    Nestle      100Grand        Choc3
    Nestle      Crunch          Choc4
    Hershey's   KitKat          Choc5
    Hershey's   Reeses          Choc2
    Hershey's   Mounds          Choc1
    Mars        Twix            Choc3
    Mars        Vaid            Choc2",
  header = TRUE,
  stringsAsFactors = FALSE)

ui <- fluidPage(
  selectInput("Select1","select1",unique(candyData$Brand)),
  selectInput("Select2","select2",choices = NULL),
  selectInput("Select3","select3",choices=NULL ))

server <- 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]))
  }) 

}

shinyApp(ui = ui, server = server)