title: Extracting values of input widgets after updating dynamic UI using renderUI()
body: <p>I have successfully updated UI dynamically through renderUI(). I have a long list of inputs to choose from. The check boxes are used to dynamically add numeric inputs. So, to implement this, I used lapply. However, I have used values of selected check boxes in checkboxgroup itself to populate IDs of the dynamically added numerical input instead of using paste(input, i) in lapply.</p>
  
  <p><strong><em>ui code snippet :</em></strong></p>
  
  <pre><code>checkboxGroupInput(inputId = "checkboxgrp", label = "Select types",
                         choices = list("ELECTAPP","NB W $","PUR","MANUAL LTR","REDEMPTION","NB W TRANSFER","NB WOUT $","OUTPUT")),
  ...    
  fluidRow(column(12, verbatimTextOutput("value")))
  ...
  uiOutput("numerics")
  </code></pre>
  
  <p><strong><em>server code snippet :</em></strong> </p>
  
  <pre><code>renderUI({
      numInputs &lt;- length(input$checkboxgrp)
  
      if(numInputs==0){
        wellPanel("No transaction selected")
      }
      else{
        lapply(1:numInputs, function(i){
          x[i]=input$checkboxgrp[i]
          list(numericInput(input$checkboxgrp[i], min = 0, label = input$checkboxgrp[i], 
                           value= input[[x[i]]] ))
        })
      }
    })
    output$value &lt;- renderPrint({
      numInputs &lt;- length(input$checkboxgrp)
      lapply(1:numInputs, function(i){
        print(input[[x[i]]]) ## ERROR
      })
    })
  </code></pre>
  
  <p>I have used <code>input[[x[i]]]</code> as to instantiate value to be retained after adding or removing a numeric input. But, I want to extract values from <code>input$x[i]</code> or <code>input[[x[i]]]</code> into a vector for further use which I'm unable to do.</p>
  
  <p>*<code>ERROR:Must use single string to index into reactivevalues</code> </p>
  
  <p>Any help is appreciated.
  <hr></p>
  
  <h2>EDIT</h2>
  
  <p>using 3 different ways of extracting values from input generate 3 different errors: 
  Using <code>print(input$x[i]) # ERROR</code></p>
  
  <pre><code>NULL
  NULL
  NULL
  NULL
  [[1]]
  NULL
  
  [[2]]
  NULL
  
  [[3]]
  NULL
  
  [[4]]
  NULL
  </code></pre>
  
  <p>Using <code>print(input[[x[i]]]) # ERROR</code></p>
  
  <pre><code>Must use single string to index into reactivevalues
  </code></pre>
  
  <p>Using <code>print('$'(input, x[i])) # ERROR</code></p>
  
  <pre><code>invalid subscript type 'language'
  </code></pre>