Question

I have a lot of elements with the same class. These elements are divided into groups by means of attribute “data-xxx“

<div class="myclass" data-n="group1"></div>
<div class="myclass" data-n="group1"></div>
<div class="myclass" data-n="group1"></div>
.... 
<div class="myclass" data-n="group2"></div>
<div class="myclass" data-n="group2"></div>
...
<div class="myclass" data-n="group3"></div>
...
...

How to perform a function on each item, but only once in each group using something like this?

$('.myclass').each(function(){

/// My function

});

Answer 1

Working example: http://jsfiddle.net/5sKqU/1/

$(document).ready(function() {
    var group = {}; //an object that we're going to use as a hash  
    $('.myclass').each(function(){ 
        if (group[$(this).attr('data-n')] != true) {
            group[$(this).attr('data-n')] = true;

            //do something here once per each group
            alert('Group: '+ $(this).attr('data-n'));
        }
    }); 
});

I’m assuming that you only need this to run once on page load. If you could share more about your requirements, I can show you what changes you’ll need to make.