r - Pre-select rows of a dynamic DT in shiny

Question

This question is the more dynamic version of this.

I have a DT in shiny app that could be empty at initialization. I'd like to pre-select all rows in DT. My first try is like this:

library(shiny)
library(DT)
shinyApp(
  ui = fluidPage(
    fluidRow(
      radioButtons("select", "", c("none", "iris")),
      DT::dataTableOutput('x1')
    )
  ),
  server = function(input, output, session) {
    data <- reactive({
      if (input$select == "none") {
        return(NULL)
      } else if (input$select == "iris"){
        return(iris)
      }
    })
    output$x1 = DT::renderDataTable(
      data(), server = FALSE,
      selection = list(mode = 'multiple', selected = seq_len(nrow(data())))
    )
  }
)

It did selection right but there is an error of Warning: Error in seq_len: argument must be coercible to non-negative integer in the beginning. I think that's because seq_len cannot take an NULL input. Interestingly after the initialization, switching back and forth doesn't generate new errors.

I tried this version to use an reactive value for rows vector, with empty result for empty input:

library(shiny)
library(DT)
shinyApp(
  ui = fluidPage(
    fluidRow(
      radioButtons("select", "", c("none", "iris")),
      DT::dataTableOutput('x1')
    )
  ),
  server = function(input, output, session) {
    data <- reactive({
      if (input$select == "none") {
        return(NULL)
      } else if (input$select == "iris"){
        return(iris)
      }
    })
    all_rows <- reactive({
      df <- data()
      if (is.null(df)) {
        return(seq_len(0))
      } else {
        return(seq_len(nrow(df)))
      }
    })
    output$x1 = DT::renderDataTable(
      data(), server = FALSE,
      selection = list(mode = 'multiple', selected = all_rows()))
  }
)

However this doesn't work. I tried another version which used a modified seq_len but it also doesn't work.

library(shiny)
library(DT)
seq_len_null_check <- function(len){
  if (is.null(len)){
    return(integer(0))
  } else {
    return(seq_len(len))
  }
}
shinyApp(
  ui = fluidPage(
    fluidRow(
      radioButtons("select", "", c("none", "iris")),
      DT::dataTableOutput('x1')
    )
  ),
  server = function(input, output, session) {
    data <- reactive({
      if (input$select == "none") {
        return(NULL)
      } else if (input$select == "iris"){
        return(iris)
      }
    })
    output$x1 = DT::renderDataTable(
      data(), server = FALSE,
      selection = list(mode = 'multiple', selected = seq_len_null_check(nrow(data())))
    )
  }
)

How can I remove the error in first version, or make the 2nd, 3rd version work?

Answer 1

To allow reactive on selected evaluation, you need to call datatable from within renderDataTable:

output$x1 = renderDataTable(
              datatable( data(),
                         selection = list(mode = 'multiple', selected = all_rows())), 
              server = FALSE)