actionButton_as_switch.R

library(shiny)

shiny::shinyApp(
  ui = sidebarLayout(
    sidebarPanel(
      actionButton("one",   "One"),
      actionButton("two",   "Two"),
      actionButton("three", "Three"),
      actionButton("four",  "Four")
    ),
    mainPanel(verbatimTextOutput("view"))
  ),
  server = function(input, output, session){
    
    button_cache <- reactiveVal({
        rep(FALSE, 4)
    })
    
    selected <- reactiveVal()
    
    buttons <- reactive({
      c(input$one,
        input$two,
        input$three,
        input$four)
    })
    
    observe({
      
      selected(
        as.logical(
          buttons() - isolate(button_cache())
        )
      )
      
      button_cache(
        buttons()
      )
      
    })
    
    output$view <- renderPrint({
      
      selected()
      
    })
  }
)