基于另一个updateselectInput()的值更新updateselectInput()

在下面的应用程序中,我想更新第二个 updateSelectInput() 为了排除第一个选项中选择的值,我选择了 updateSelectInput() 上传文件后。通常,该文件会上传用于闪亮小部件值的数据集。

## app.R ##
library(shiny)
library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(
    fileInput("file1", "Choose CSV File", accept = ".csv"),

    selectInput("col","Pick a column to change its name",
                choices = colnames(iris)[-c(1)]),
    selectInput("col2","Pick a column to change its name",
                choices = colnames(iris)[-c(1)])

  ),
  dashboardBody(
    
    )
)

server <- function(session,input, output) {
  
  observeEvent(input$file1, {
    updateSelectInput(session, "col", label = "Select target country", choices = colnames(iris)[-c(1)])
    ex_names <- colnames(iris)[-1]
    ex_names <- ex_names[! ex_names %in% input$col]
    updateSelectInput(session, "col2", label = "Select reference countries", choices =colnames(iris)[-c(1)] )  

    
  })
  
 
  
}

shinyApp(ui, server)