jquery - add a class to first element in array -

i have simple question jquery array elements...

<div id="holder">            <div class="a">a</div>     <div class="a">a</div>     <div class="a">a</div>     <div class="b">b</div>     <div class="b">b</div>     <div class="b">b</div>     <div class="b">b</div>     <div class="c">c</div>     <div class="c">c</div>     <div class="c">c</div>     <div class="c">c</div>     <div class="c">c</div> </div> 

and js:

var klassenarray = $("#holder").find("[class]").map(function() {      return this.classname;    }).get(); alert(klassenarray); 

gives me:

a,a,a,b,b,b,b,c,c,c,c,c 

now need add class called first every element same classname. that:

<div id="holder">            <div class="a first">a</div>     <div class="a">a</div>     <div class="a">a</div>     <div class="b first">b</div>     <div class="b">b</div>     <div class="b">b</div>     <div class="b">b</div>     <div class="c first">c</div>     <div class="c">c</div>     <div class="c">c</div>     <div class="c">c</div>     <div class="c">c</div> </div> 

to achieve can take array, unique values, loop through , use first() method retrieve first elements given class. try this:

var klassenarray = $("#holder").find("[class]").map(function() {    return this.classname;  }).get();    $.unique(klassenarray).foreach(function(c) {    $('.' + c).first().addclass('first');  });

.first { color: #c00; }

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>  <div id="holder">    <div class="a">a</div>    <div class="a">a</div>    <div class="a">a</div>    <div class="b">b</div>    <div class="b">b</div>    <div class="b">b</div>    <div class="b">b</div>    <div class="c">c</div>    <div class="c">c</div>    <div class="c">c</div>    <div class="c">c</div>    <div class="c">c</div>  </div>