Limit row selection in DT Table in Shiny - r

Question

I am currently trying to limit my selection in a DataTable in Shiny to just two rows - I want the table to not allow the user to click on more than rows (but also to have the ability to deselect them afterwards).
library(DT)
shinyApp(
ui = fluidPage(
fluidRow(
column(12,
dataTableOutput('table')
)
)
),
server = function(input, output) {
output$table <- DT::renderDataTable(iris,
options = list(selection = "multiple")
)
}
)
The row selection is currently on multiple mode, which works, but I don't want the selection to exceed two rows.

Answer 1

Update: Does not seem to work anymore, since 04.2022 or earlier.
You could either solve it via javascript, which you may have seen already:
Limit row selection to 3 in datatables
Or you update the datatable in Shiny:
library(DT)
library(shiny)
shinyApp(
ui = fluidPage(
fluidRow(
column(12,dataTableOutput('tbl'))
)
),
server = function(input, output) {
reset <- reactiveValues(sel = "")
output$tbl <- DT::renderDataTable({
input$tbl_rows_selected
datatable(iris, selection = list(mode = 'multiple', selected = reset$sel))
})
observe({
if(length(input$tbl_rows_selected) > 2){
reset$sel <- setdiff(input$tbl_rows_selected, input$tbl_row_last_clicked)
}else{
reset$sel <- input$tbl_rows_selected
}
})
}
)
This solution might be less clean, but a bit easier to understand.

Answer 2

It's not exactly what you want but I've changed a bit Tonio's answer, it may help someone else.
library(DT)
library(shiny)
shinyApp(
ui = fluidPage(
fluidRow(
column(12,dataTableOutput('tbl'))
),
textOutput('selected_rows')
),
server = function(input, output) {
reset <- reactiveValues(sel = "")
output$tbl <- DT::renderDataTable({
datatable(iris, selection = list(mode = 'multiple', selected = reset$sel))
})
observe({
if(length(input$tbl_rows_selected) > 2){
reset$sel <- NULL
}else{
reset$sel <- input$tbl_rows_selected
}
})
output$selected_rows <- renderText({input$tbl_rows_selected})
}
)