MultiSelectPLCom.cmp

<aura:component >
    <aura:attribute name="allvalues" type="List" />
    <aura:attribute name="selValues" type="List" />
    <aura:attribute name="selectedValue" type="String"/>
    <aura:attribute name="unselectedValue" type="String"/>
    <aura:handler name="init" value="this" action="{!c.init}" />
    <div class="slds-page-header">
      <div class="slds-media">
        <div class="slds-media__figure">
          
        </div>
        <div class="slds-media__body">
          <h1 class="slds-page-header__title slds-truncate slds-align-middle" title="Select The value from one list and pass it in another">
            	Select The value from one list and pass it in another
            </h1>
          <p class="slds-text-body_small slds-line-height_reset"></p>
        </div>
      </div>
    </div>
    <br/><br/>
     <lightning:select name="mySelect" label="Select a Number:" value="{!v.selectedValue}" aura:id="mySelect">
        <option value="">choose one...</option>
        <aura:iteration items="{!v.allvalues}" var="allkey" >
            <option value="{!allkey}">{!allkey}</option>
    	</aura:iteration>
    </lightning:select>
    <br/><br/>
    <lightning:button variant="brand" label="Add" onclick="{! c.add }" />
    <lightning:button variant="destructive" label="Return" onclick="{! c.returnNumber }" />
    <br/><br/>
    <lightning:select name="selectItem" label="Return a Number" value="{!v.unselectedValue}" aura:id="unSelect">
        <option value="">choose one...</option>
        <aura:iteration items="{!v.selValues}" var="allkey" >
            <option value="{!allkey}">{!allkey}</option>
    	</aura:iteration>
    </lightning:select>
</aura:component>