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我正在开发Shiny应用程序。我同时使用renderUI和removeUI时遇到问题。input$sumcol如果我在input$aggrselectInput中选择“ sum”聚合函数，我想生成一个包含整数或数字列（）的selectInput ui 。这是我的代码：

# elements in ui
selectInput("vars", "data to display:", choices = NULL, multiple = TRUE, selected = NULL),
selectInput("aggr", "aggregation function:", choices = c("count", "sum"), selected = NULL),
uiOutput("sumcolcontrol")

#server

## create/delete #sumcoldiv  based on selection of input$aggr
observeEvent(input$aggr, {

  if(input$aggr == "sum") { 
    # create sumcol select UI
    output$sumcolcontrol <- renderUI({
      # add a div that contains input$sumcol, so it's easy to remove the div by id later
      tags$div(id = "sumcoldiv",selectInput("sumcol", "column …