与依赖项一起闪亮的renderUI n次

Question

我正在尝试渲染相同的UI n次，其中时间t的每个元素ui都依赖于前一个（t-1）。这是我的reprex在n = 2上工作的地方，其中我手动编写了renderUI：

library(shiny)

choices0 <- LETTERS[1:10]
ui <- fluidPage(
  tagList(
    checkboxGroupInput("cbGI_0", label = 0, inline = TRUE,
                       choices = choices0, 
                       selected = choices0),
    uiOutput("cbGI_ui_1")
  )

)

server <- function(input, output) {

  output$cbGI_ui_1 <- renderUI({
    choices <- choices0[!choices0 %in% input$cbGI_0]
    if (length(choices) > 0){
      tagList(
        checkboxGroupInput("cbGI_1", label = 1, inline = TRUE, 
                           choices = choices, 
                           selected = choices),
        uiOutput("cbGI_ui_2")
      )
    }
  })

  output$cbGI_ui_2 <- renderUI({
    choices <- choices0[!choices0 %in% c(input$cbGI_0, input$cbGI_1)]
    if (length(choices) > 0){
      tagList(
        checkboxGroupInput("cbGI_2", label = 2, inline = TRUE, 
                           choices = choices, 
                           selected = choices),
        uiOutput("cbGI_ui_3")
      )
    }
  })

  #and so on

}

shinyApp(ui = ui, server = server)

我的问题是关于做相同的事情，但时间不限。我尝试这样编码，但不起作用：

library(shiny)

choices0 <- LETTERS[1:10]
ui <- fluidPage(
  tagList(
    checkboxGroupInput("cbGI_0", label = 0, inline = TRUE,
                       choices = choices0, 
                       selected = choices0),
    uiOutput("cbGI_ui_1")
  )

)

server <- function(input, output) {

  n <- reactive({
    length(sapply(names(input), grepl, pattern = "cbGI_[0-9]*$"))
  })

  observe({
    for (i in seq_len(n())){
      output[[paste0("cbGI_ui_", i)]] <- renderUI({
        choices <- choices0[!choices0 %in% 
                              sapply(seq_len(i), function(k){
                                input[[paste0("cbGI_", k-1)]]
                              })
                            ]

        if (length(choices) > 0){
          tagList(
            checkboxGroupInput(paste0("cbGI_", i), label = i, inline = TRUE, 
                               choices = choices, 
                               selected = choices),
            uiOutput(paste0("cbGI_ui_", i+1))
          )
        }
      })
    }
  })

}

shinyApp(ui = ui, server = server)

似乎我陷入了无限循环...知道如何解决我的问题吗？