bind to filtered object property knockout nested foreach

Question

I am trying to understand $parent, $data and stuck trying to filter out object array based on the $parent value.

<p>My kids:</p>
    <ul data-bind="foreach: kids">
        <li> <span data-bind="text: $data" ></span>      
              <ul data-bind="foreach: grandKids.filter(function (obj) { return obj.mother === $parent })">
                 <li><span data-bind="text: $data.name"></span></li>                      
             </ul>
         </li>
      </ul>


    <script src="Scripts/knockout-3.4.1.js"></script>
    <script>
        var vm = {
            name : ko.observable("Anjan"),
            age: ko.observable(40),
            kids: ["Mira", "Teresa"],
            grandKids: [
                         { name: "Andy", mother: "Mira" }, 
                         { name: "Alice", mother: "Mira" }, 
                         { name: "Alex", mother: "Teresa" }, 
                         { name: "Abby", mother: "Teresa" }
                       ]
        };

Answer 1

For anyone, who ran into this kind of issue binding an element into a filtered set, I am sure there are other ways of doing it to, but the way i resolved this was by using a container-less KO binding, as below:

<ul data-bind="foreach: kids">
                <li>                         
                    <span data-bind="text: $data.name" > </span>  
                     <button data-bind="click: $parent.removeKid">Remove (moved out)</button> 
                     <button data-bind="click: $root.addGrandKid" style="float:right;">Just had a baby</button>

                    <ul data-bind="foreach: vm.grandKids">
                        <!--ko if: $parent.name() == $data.mother() -->
                            <li>                    
                                <!--ko $data.name() --><!-- /ko -->

                            </li>  
                        <!-- /ko-->                    
                    </ul> 

                  </li>            
            </ul>

I am still unclear as to why I needed to fully qualify the grandKids property as vm.grandKids in the UI binding for the unordered list.