How to make R Shiny DataTable table give columns drop down menus with all possible values populated

I have the following code that generates a R Shiny datatable. There are 开发者_C百科currently free text input boxes for each column that allows you filter the contents. I have been struggling with figuring out how to make these drop down menu filters, that would have all possible options for that given column populated, instead.

I know this current column level search functionality is coming from filter = "top", but I'm struggling to even find documentation on the other possible inputs for this parameter.

Full code below:

ui <- fluidPage(
  downloadButton("download_data", "Download filtered data as CSV"),
  DT::dataTableOutput("data"),
)

# Define server logic
server <- function(input, output) {
  filtered_data <- reactive({
    if (length(input$columns) == 0) {
      return(dataframe)
    } else {
      dataframe %>%
        filter_at(vars(input$columns), any_vars(grepl(input$search, ., ignore.case = TRUE)))
    }
  })
  
  output$data <- DT::renderDataTable({
    DT::datatable(filtered_data(), filter = "top", escape = FALSE, rownames = FALSE)
  })
  
  output$download_data <- downloadHandler(
    filename = paste("Land_Use_Data_",toString(Sys.Date()), ".csv", sep = ""),
    content = function(file) {
      write.csv(filtered_data(), file, row.names = FALSE)
    }
  )
}

shinyServer(function(input, output, session) {
  reactiveValuesToList(session)$search <- ""
})

shinyApp(ui = ui, server = server)

If you want a dropdown list for a column, convert this column to a factor. Example:

dat <- iris
dat$Sepal.Length <- factor(dat$Sepal.Length)

DT::datatable(dat, filter = "top")