R shiny observe for row deselection dataTable

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I have a shiny app that has a DT::renderDataTable, the user can select a row in the datatable.

The following bit of code will only print FALSE (when a row is selected):

observeEvent(input$segment_library_datatable_rows_selected, {

How do I get it to print when a row is also deselected? (The print value would be TRUE)

As I understand a working minimal example would be the following (sel() reactive is TRUE if a row in datatable is selected):

ui <- fluidPage(
server <- function(input, output) {
  # Output iris dataset
  output$datatable <- DT::renderDataTable(iris, selection = "single")
  # Reactive function to determine if a row is selected
  sel <- reactive({!is.null(input$datatable_rows_selected)})  
  # Output result of reactive function sel
  output$any_rows_selected <- renderText({
    paste("Any rows selected: ", sel())
shinyApp(ui, server)

observeEvent not fired with datatable (DT) deselection : rshiny, observeEvent not fired with datatable (DT) deselection. Hello, I'm fairly new to shiny,. I'm trying to figure out how I can get the event from a deselection of a row in  Shiny's reactive programming framework is primarily designed for calculated values (reactive expressions) and side-effect-causing actions (observers) that respond to any of their inputs changing. That's often what is desired in Shiny apps, but not always: sometimes you want to wait for a specific action to be taken from the user, like clicking an actionButton() , before calculating an expression or taking an action.

Alternatively you can use observe() which will respond to any hits to the input$datatable_rows_selected, including NULL.

To repurpose Kristoffer W. B.'s code:

ui <- fluidPage(

server <- function(input, output) {
  # Output iris dataset
  output$testtable<- DT::renderDataTable(iris, selection = "single")

  # Observe function that will run on NULL values
  an_observe_func = observe(suspended=T, {
                      #do stuff here

  #start the observer, without "suspended=T" the observer 
  #  will start on init instead of when needed

shinyApp(ui, server)

A few things to note:

1) I found it best to start the observer in suspended mode, that way it doesn't start when the program initializes. You can turn it on whenever you want it to... observe... (such as after you render the datatable, or before you'd like to start tracking selections).

2) Use isolate to stop the observer from tracking multiple elements. in this case the observer should only react to input$testtable_rows_selected, instead of everything else occurring. The symptom of this problem is that your observer fires multiple times on a single change.

Using DT in Shiny, Here is a minimal example of (client-side) DataTables in Shiny using the convenience functions Clicking on the table body will select/deselect rows. Shiny (>= v1.10.2) currently uses DataTables v1.10. If you have used DataTables in Shiny before (specifically, before Shiny v0.10.2), you may need to change some parameter names for your DataTables, because Shiny (<= v0.10.1) was using DataTables v1.9, and DataTables v1.10 has changed the parameter names.

observeEvent(input$selected,ignoreNULL = FALSE,{...})

ignoreNULL is defaulted to TRUE. Set to FALSE to have the event observed upon deselection.

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  • I guess observeEvent does not trigger when input$segment_library_datatable_rows_selected is NULL. Have you tried a standard observe or reactive function (e.g. sel <- reactive({is.null(input$segment_library_datatable_rows_selected)})). Also please specify if your DT has selection of multiple rows enabled and if you want to detect any changes in the row selection (e.g. also going from 3 to 2 selected rows).
  • @KristofferWintherBalling DT selection is set to single, and the above works perfectly.
  • have you tried simply: print(!is.null(input$segment_library_datatable_rows_selected))