Extracting values of input widgets after updating dynamic UI using renderUI()
<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>