grouping draggable objects with jquery-ui draggable

$(function() {

  $('#dragSource li').draggable({
    helper: function() {
      var selected = $('#dragSource input:checked').parents('li');
      if (selected.length === 0) {
        selected = $(this);
      }
      var container = $('<div/>').attr('id', 'draggingContainer');
      container.append(selected.clone());
      return container;
    }
  });

  $('#dropTarget').droppable({
    tolerance: 'pointer',
    drop: function(event, ui) {
      $(this).append(ui.helper.children());
    }
  });

  $('#selectAll').click(function() {
    $('#dragSource input').prop('checked', true);
    return false;
  });

  $('#selectNone').click(function() {
    $('#dragSource input').prop('checked', false);
    return false;
  });

  $('#selectInvert').click(function() {
    $('#dragSource input').each(function() {
      var $this = $(this);
      if ($this.prop('checked')) {
        $this.prop('checked', false);
      } else {
        $this.prop('checked', true);
      }
    });
    return false;
  });
});

body {
  font-family: sans-serif;
  overflow-x: hidden;
}
div {
  margin: 5px;
  padding: 0;
}
ul {
  margin: 0;
  padding: 0;
}
li {
  list-style: none;
  padding: 0;
  margin: 0;
  float: left;
  white-space: nowrap;
}
#selectActions span,
#selectActions li {
  float: left;
  padding: 5px;
}
.droppableContainer {
  width: 48%;
  float: left;
  min-height: 200px
}
.droppableContainer li {
  height: 90px;
  width: 110px;
  margin: 2px;
  background-color: white;
  padding-bottom: 4px;
}
.droppableContainer img {
  width: 90px;
  max-height: 90px;
  max-width: 90px;
  width: 90px;
  vertical-align: middle;
}
.droppableContainer input {
  height: 90px;
  vertical-align: middle;
}
#draggingContainer {
  width: 48%;
}
#draggingContainer input {
  visibility: hidden;
}
#dropTarget {
  border: 3px dashed grey;
}
#dropTarget input {
  visibility: hidden;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/themes/smoothness/jquery-ui.css">
<script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.11.4/jquery-ui.min.js"></script>

<div id="selectActions">
  <span>Select:</span>
  <ul>
    <li><a id="selectAll" href="#">all</a>
    </li>
    <li><a id="selectNone" href="#">none</a>
    </li>
    <li><a id="selectInvert" href="#">invert</a>
    </li>
  </ul>
</div>
<div style="clear:left;">
  <div id="dragSource" class="droppableContainer">
    <ul>
      <li>
        <img src="http://imgs.xkcd.com/comics/drapes.png" /><input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/misusing_slang.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/donner.jpg" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/a_new_captcha_approach.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/bug.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/open_source.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/tag_combination.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/a_simple_plan.jpg" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/it_might_be_cool.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/hedgeclipper.jpg" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/pep_talk.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/regular_expressions.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/pwned.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/post_office_showdown.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/im_an_idiot.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/pointers.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/chess_photo.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/50_ways.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/e_to_the_pi_times_i.png" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/self-reference.jpg" />
        <input type="checkbox" />
      </li>
      <li>
        <img src="http://imgs.xkcd.com/comics/starwatching.png" />
        <input type="checkbox" />
      </li>
    </ul>
  </div>

  <div id="dropTarget" class="droppableContainer">
  </div>
</div>