How to Set Selected value in Multi-Value Select in Jquery-Select2.?

Well actually your only need $.each to get all values, it will help you jsfiddle.net/NdQbw/5

<div class="divright">
            <select id="drp_Books_Ill_Illustrations" class="leaderMultiSelctdropdown Books_Illustrations" name="drp_Books_Ill_Illustrations" multiple="">
                <option value=" ">No illustrations</option>
                <option value="a" selected>Illustrations</option>
                <option value="b">Maps</option>
                <option value="c" selected>selectedPortraits</option>
            </select>
    </div>

<div class="divright">
        <select id="drp_Books_Ill_Illustrations1" class=" Books_Illustrations" name="drp_Books_Ill_Illustrations" multiple="">
            <option value=" ">No illustrations</option>
            <option value="a">Illustrations</option>
            <option value="b">Maps</option>
            <option value="c">selectedPortraits</option>
        </select>
</div>

<button class="getValue">Get Value</button>
<button  class="setValue"> Set  value </button>

<div class="divright">
        <select id="drp_Books_Ill_Illustrations2" class="leaderMultiSelctdropdown Books_Illustrations" name="drp_Books_Ill_Illustrations" multiple="">
            <option value=" ">No illustrations</option>
            <option value="a" selected>Illustrations</option>
            <option value="b">Maps</option>
            <option value="c" selected>selectedPortraits</option>
        </select>
</div>

<div class="divright">
        <select id="drp_Books_Ill_Illustrations3" class=" Books_Illustrations" name="drp_Books_Ill_Illustrations" multiple="">
            <option value=" ">No illustrations</option>
            <option value="a">Illustrations</option>
            <option value="b">Maps</option>
            <option value="c">selectedPortraits</option>
        </select>
</div>

<button class="getValue1">Get Value</button>
<button  class="setValue1"> Set  value </button>

The script:

 var selectedValues = new Array();
    selectedValues[0] = "a";
    selectedValues[1] = "c";

$(".getValue").click(function() {
    alert($(".leaderMultiSelctdropdown").val());
});
$(".setValue").click(function() {
   $(".Books_Illustrations").val(selectedValues);
});

$('#drp_Books_Ill_Illustrations2, #drp_Books_Ill_Illustrations3').select2();


$(".getValue1").click(function() {
    alert($(".leaderMultiSelctdropdown").val());
});

$(".setValue1").click(function() {
    //You need a id for set values
    $.each($(".Books_Illustrations"), function(){
            $(this).select2('val', selectedValues);
    });
});