How can I sort an array, yet exclude certain elements (to be kept at the same position in the array)

Question

This will be implemented in Javascript (jQuery) but I suppose the method could be used in any language.

I have an array of items and I need to perform a sort. However there are some items in the array that have to be kept in the same position (same index).

The array in question is build from a list of <li> elements and I'm using .data() values attached to the list item as the value on which to sort.

What approach would be best here?

<ul id="fruit">
  <li class="stay">bananas</li>
  <li>oranges</li>
  <li>pears</li>
  <li>apples</li>
  <li class="stay">grapes</li>
  <li>pineapples</li>
</ul>

<script type="text/javascript">
    var sugarcontent = new Array('32','21','11','45','8','99');
    $('#fruit li').each(function(i,e){
       $(this).data('sugar',sugarcontent[i]);
    })
</script>

I want the list sorted with the following result...

<ul id="fruit">
      <li class="stay">bananas</li> <!-- score = 32 -->
      <li>pineapples</li> <!-- score = 99 -->
      <li>apples</li> <!-- score = 45 -->
      <li>oranges</li> <!-- score = 21 -->
      <li class="stay">grapes</li> <!-- score = 8 -->
      <li>pears</li> <!-- score = 11 -->
  </ul>

Thanks!

Answer 1

Algorithm is:

• Extract and sort items not marked with stay

• Merge stay items and sorted items

  var sugarcontent = new Array(32, 21, 11, 45, 8, 99);
  
  var items = $('#fruit li');
  
  items.each(function (i) {
      $(this).data('sugar', sugarcontent[i]);
      // Show sugar amount in each item text - for debugging purposes
      if ($(this).hasClass('stay'))
          $(this).text("s " + $(this).text());
      else
          $(this).text(sugarcontent[i] + " " + $(this).text());
  });
  
  // Sort sortable items
  var sorted = $(items).filter(':not(.stay)').sort(function (l, r) {
      return $(l).data('sugar') - $(r).data('sugar');
  });
  
  // Merge stay items and sorted items
  var result = [];
  var sortedIndex = 0;
  
  for (var i = 0; i < items.length; i++)
      if (!$(items[i]).hasClass('stay')) {
          result.push(sorted[sortedIndex]);
          sortedIndex++;
      }
      else
          result.push(items[i]);
  
  // Show result
  $('#fruit').append(result);