title: Convert Csv to JSON with nested array
body: <p>I have a CSV file  </p>
  
  <pre><code>group, first, last
  fans, John, Smith
  fans, Alice, White
  students, Ben, Smith
  students, Joan, Carpenter
  ...
  </code></pre>
  
  <p>The Output JSON file needs this format:</p>
  
  <pre><code>[
  {
    "group" : "fans",
    "user" : [
      {
        "first" : "John",
        "last" :  "Smith"
      },
      {
        "first" : "Alice",
        "last" :  "White"
      }
    ]
  },
  {
    "group" : "students",
    "user" : [
      {
        "first" : "Ben",
        "last" :  "Smith"
      },
      {
        "first" : "Joan",
        "last" :  "Carpenter"
      }
    ]
  }
  ]
  </code></pre>