jQuery sorting of div elements based on count, and date/time (timestamp)

Question

I currently use the sort function to sort my div elements based on the count value. Here\'s how it\'s being done now: (I\'m not sure if it\'s an efficient method or not..)

Answer 1

Performance:

I'd highly recommend to cache the wrapped set before performing a sort().

var $items = $('#list .list_item');
$items.sort(sortDescending);

That should give sizzle / your DOM a break like bigtime.

To link your timestamp value aswell, you have to extend your sorting.

function sortDescending(a, b) {
  var a_count = parseInt((a).find(".count").text(), 10),
      b_count = parseInt((b).find(".count").text(), 10),
      a_time  = parseInt((a).find(".timestamp").text(), 10),
      b_time  = parseInt((b).find(".count").text(), 10);

  return (a_count < b_count && a_time > b_time);
};

While writting this I actually realized that I wouldn't parse those values through element content. If you generate those nodes somewhere dynamically, it's maybe a better idea to use jQuerys $.data() method to store date and use/access that within your sorting method.

Answer 2

Only the sort comparator function needs to change. I'm sure there are plugins available to do this, and you might want to take a look at them, but implementing what you want is fairly trivial. The sortDescending method gets two divs each time, and comparison must follow the criteria you've specified:

1. First by count
2. If count is equal, then by timestamp
3. If timestamps are equal, then return 0

Here's the ugly straightforward non-optimized version:

function sortDescending(a, b) {
    if(getCount(a) < getCount(b)) {
        return -1;
    }
    else if(getCount(a) > getCount(b)) {
        return 1;
    }
    else if(getTimestamp(a) < getTimestamp(b)) {
        return -1;
    }
    else if(getTimestamp(a) > getTimestamp(b) {
        return 1;
    }
    else {
        return 0;
    }
}

If you see the if-else structure, it may seem obvious that you can genericize this approach to be able to handle any type of custom ordering. So here's a jab at a sortBy method that takes in a number callback functions, where each callback defines one sorting criteria.

function sortBy() {
    var callbacks = arguments;

    return function(a, b) {
        for(var i = 0; i < callbacks; i++) {
            var value = callbacks[i](a, b);
            if(value != 0) {
                return value;
            }
        }
        return 0;
    };
}

Then pass all criteria's as callbacks to this sortBy function. Here's a rough example for your code:

function compareCount(a, b) {
    return getCount(a) - getCount(b);
}

function compareTimestamp(a, b) {
    return getTimestamp(a) - getTimestamp(b);
}

$("selector").sort(sortBy(compareCount, compareTimestamp));

And while we are at it, let's also make a jQuery plugin out of this. It will have a nice and easy interface:

$("parent selector").sortBy("child selector 1", "child selector 2", ...);

The idea is to pass a jQuery selector that will select a node whose text will determine the value to sort by. We will give integers a higher priority and first try to sort numerically if both values are so, otherwise do a regular comparison.

jQuery.fn.sortBy = function() {  
    var selectors = arguments;

    this.sort(function(a, b) {
        // run through each selector, and return first non-zero match
        for(var i = 0; i < selectors.length; i++) {
            var selector = selectors[i];

            var first = $(selector, a).text();
            var second = $(selector, b).text();

            var isNumeric = Number(first) && Number(second);
            if(isNumeric) {
                var diff = first - second;
                if(diff != 0) {
                    return diff;
                }
            }
            else if(first != second) {
                return first < second ? -1 : 1;
            }
        }

        return 0;
    });

    this.appendTo(this.parent());

    return this;
};

Use as

$('#list .list_item').sortBy('.count', '.timestmap');

See an example of the plugin here.

Btw, none of this will actually sort the elements in the document itself. See this question for how to do that.