title: What does shiny_callback capture in rbokeh?
body: <p>I'm trying to use the tool_lasso_select feature in rbokeh. What I would like is for the user to use the tool to select a group of points in a scatterplot and summary statistics of the group of points selected would be created as a result in the next panel of a shiny tabBox. My primary question is:</p>
  
  <p>What exactly is captured by the shiny_callback option? </p>
  
  <p>This is an example of the type of figure I'm creating:</p>
  
  <pre><code>figure() %&gt;%
  ly_points(x = cty, y = hwy, data = mpg,
          hover = c(cty, hwy), lname = "points") %&gt;%
  tool_hover(shiny_callback(id = "hover_info"), "points") %&gt;%
  tool_tap(shiny_callback(id = "tap_info"), "points") %&gt;%
  tool_box_select(shiny_callback(id = "selection_info"), "points")
  </code></pre>
  
  <p>What exactly are the contents placed in the "selection_info" id and how could I extract that information? I'm just not sure what the next block of code I could write that would take the information captured by the lasso_tool. The most I can find in the documentation is the example used but output seems to only be an index number. </p>
  
  <p>UPDATE:</p>
  
  <p>Thanks for adding a reproducible example. My apologies. I've added a little more to it below:</p>
  
  <pre><code>library("dplyr")
  library("rbokeh")
  library("shiny")
  
  attach(mtcars)
  
  server &lt;- shinyServer(function(input,output){
  
    output$myChart &lt;- renderRbokeh({
      print(paste0("now rendering!"," ",date()))
      input$myText
      figure() %&gt;%
        ly_points(x = mtcars$cyl, y = mtcars$hp, data = mtcars,
                  hover = c(mtcars$cyl, mtcars$hp), lname = "points") %&gt;%
        tool_hover(callback = shiny_callback(id = "hover_info"), "points") %&gt;%
        tool_tap(callback = shiny_callback(id = "tap_info"), "points") %&gt;%
        tool_box_select(callback = shiny_callback(id = "selection_info"), "points")
    })
  
    output$selection_summary &lt;- renderText({
      input$selection_info
    })
  
  
  })
  
  ui &lt;- shinyUI(
    fluidPage(
  
      rbokehOutput(outputId = "myChart", width = "400px", height = "400px"),
      textInput(inputId="myText",label="Input Text please."),
      textInput(inputId="selection_info",label="Selection info"),
  
      textOutput("selection_summary")
    )
  )
  
  shinyApp(server = server, ui = ui)
  </code></pre>
  
  <p>So the above <code>output$selection_summary</code> does provide some type of info that is given by the tool_box_select. I'm just not sure what it is. I'd eventually like to produce a table or summary statistics on the attributes associated with the points selected by the tool. But I don't know how to figure out what it is the callback feature is capturing. I couldn't find anymore details in the documentation, unless I've missed something.</p>
  
  <p>Thanks. </p>