Q:

Selecting all values from drop down menu in Flexdashbaord

I have taken a sample code of one of the Shiny Flexdashboard. 
In the sample code there is a drop down menu to select one region at a time.
I just want to know is there a way to select all the values in the drop down menu? 
Kindly find the code in below link, 
beta.rstudioconnect.com/jjallaire/shiny-embedding
for code, click "Source Code" on the top extreme right. 
Regards,
Mohan

A:

You can do
library(shiny)
ui = fluidPage(
  selectInput("sel", NULL, letters[1:2], multiple = T),
  actionButton("but", "all")
)
server <- function(input, output, session) {
  observeEvent(input$but, {
    updateSelectInput(session, "sel", selected = letters[1:2])
  })
}
shinyApp(ui, server)

Use ?updateSelectInput to access the documentation on that function. 

