Get selected row value instead of number in shiny using DT - r

Question

Small question here: I know I can access selected rows by input$dfname_rows_selected it gives back the numbers of rows selected, but how do I read the rows names, not numbers? In my case they are generated not in the order I use them later, therefore I need to get the values inside to make it work.
edit: added example
ui <- shinyUI(fluidPage(
DT::dataTableOutput("table"),
actionButton("btn", "press me")
))
server <- function(input, output) {
observeEvent(input$btn, {
print(input$table_rows_selected)
})
output$table <- DT::renderDataTable({
mtcars %>%
datatable(selection = "multiple")
})
}
shinyApp(ui = ui, server = server)

Answer 1

Something like this:
library(shiny)
library(DT)
ui <- basicPage(
mainPanel(DT::dataTableOutput('mytable')),
textOutput("selected")
)
server <- function(input, output,session) {
mydata <- reactive({mtcars})
output$mytable = DT::renderDataTable(
datatable(mydata())
)
selectedRow <- eventReactive(input$mytable_rows_selected,{
row.names(mtcars)[c(input$mytable_rows_selected)]
})
output$selected <- renderText({
selectedRow()
})
}
runApp(list(ui = ui, server = server))

Answer 2

I don't think you can. What you could do is write a reactive, where all modifications to your dataframe take place, before creating the datatable. An example:
library(shiny)
library(DT)
ui <- shinyUI(fluidPage(
DT::dataTableOutput("table"),
textOutput("selectedcar")
)
)
server <- function(input, output,session) {
# the reactive where we filter/sort/modify the data
reactive_df <- reactive({
mtcars[order(mtcars$cyl),]
})
# This datatable uses the reactive directly, so no more modifications
output$table <- DT::renderDataTable({
DT::datatable(reactive_df())
})
# now we can get the row/rowname as follows:
output$selectedcar <- renderText({
paste0(rownames(reactive_df())[input$table_rows_selected], collapse = ", ")
})
}
shinyApp(ui, server)
Hope this helps!