JavaScript combining or grouping loop results into unique arrays

So reading through your post, it sounds like you need to pre-process your data before you attach it to the DOM:

Output you get:

Item to Publish: a , Publication Target: 1

Item to Publish: a , Publication Target: 2

Item to Publish: b , Publication Target: 7

Output you want:

Item to Publish: a , Publication Target: 1, 2

Item to Publish: b , Publication Target: 7

We can use JS object literal's key/value pairing to help accomplish this. To account for multiple values, we store an array containing values into the key/value pair.

Since I don't have access to what your items array actually returns, I just created some test data to show how it should work. JSFIDDLE: http://jsfiddle.net/biz79/pLb38t0y/

Hopefully you can adjust it to fit your purpose.

// create storage object literal and key/value vars
var storage = {};
var key,value;

// some test data
var items = [
  { "Title" : "a", "Value" : "1" },
  { "Title" : "a", "Value" : "2" },
  { "Title" : "b", "Value" : "3" } 
];

// iterate items array and populate storage
for (var i =0; i<items.length; i++) {
  key = items[i].Title;
  value = items[i].Value;

  // if the key exists in storage, add to it
  if ( key in storage ) {
    storage[key].push( value );
  }
  else {
  // if the key doesn't exist, create key and add to it
    storage[key] = [];
    storage[key].push(value);
  }
}

// iterate storage for answers
for (var prop in storage) {
    if (storage.hasOwnProperty(prop)){
      alert("Item to Publish: " + prop);
      alert("Publication Target: " + storage[prop].join(','));
    }
}

For cases like this I like to use the fact that object properties are unique. I've tried not to modify your code too much. I introduced an object, groupedItems, and used its properties for the group titles. In each of those titles I stored an array with the titles of the group.

The output is more or less the same. In a new loop (a for..in loop to iterator over the properties), you can output the key (= propety name = group title), and the joined values in the array value of that property.

function parsePData(data) {

            var xmlDoc = $j.parseXML(data.d);
            var $xml = $j(xmlDoc);
            var items = $xml.find("Page");
            userFavorites = $xml;

            // Create an object to cotnain the titles.
            var groupedItems = {};
            
            for (var i = 0; i < items.size(); i++) {
              // If the grouped object doesn't contain this title yet, add it and initialize to
              // and empty array.
              var prop = items[i].getAttribute("Title");
              if (! groupedItems.hasOwnProperty(prop))
                groupedItems[prop] = new Array();

              // Push new item onto the array.
              groupedItems[prop].push(items[i].parentNode.getAttribute("Title"));
            }
  
            var newHtml = ""
  
            // Actual output using the grouped array.
            for (var k in groupedItems)
            {
                newHtml += "<div style='margin:5px; padding:5px; border-bottom: 1px dotted #9C9C9C; font-  size:95%'><div> <b>#" + (i + 1) + ".</b>Item to Publish: " + k +

                "</div><div class='itpPub'> Publication Target: " +
                  groupedItems[k].join(',') +

                "</div></div>";