<ui:inputCheckbox label="" class="check" aura:id="master" click="{!c.checkAll}" />

                <tbody>
                    <aura:iteration items="{!v.contactNames}" var="contact">
                        <tr>
                            <td data-label="Contact Name">
                                 <ui:inputCheckbox text="{!contact.Id}" aura:id="dependent" value="" change="{!c.updateCheckboxes}"/>
                            </td>
                            <td style="right: 580px;">
                                <div class="slds-truncate">{!contact.Name}</div>
                            </td>

                        </tr>
                    </aura:iteration>
                </tbody>
            </table>

checkAll: function(component, event, helper) {
    var master = component.find("master");
    var boxPack = component.find("dependent");

    var val = master.get("v.value");

         if (val == true) {

        for (var i = 0; i < boxPack.length; i++) {
            boxPack[i].set("v.value", true);
        }
    } else {
        for (var i = 0; i < boxPack.length; i++) {
            boxPack[i].set("v.value", false);
        }
    }



},