javascript - Form validity using Angular ng-repeat -

i have angular form parsing json data.
i'm rendering using ng-repeat. however, i'm having issue in form never becomes valid when radio button in each group selected.

i suspect issue lies ng-model in each input, can't seem figure out correct way dynamically create ng-model inside ng-repeat.

form block code:

<form name="posttestform">   <alert ng-repeat="alert in alerts"           type="{{alert.type}}" close="closealert($index)">{{alert.msg}}</alert>   <div class="well question-well" ng-repeat="question in questions">     <p>       <strong>{{question.question}}</strong>     </p>     <ul>       <li ng-repeat="answers in question.answers">         <input ng-model="q[question.id]"                 type="radio" name="q{{question.id}}" value="{{answers.id}}"                 required="" data-key="{{answers.iscorrect}}" />{{answers.answer}}       </li>     </ul>   </div>   <button type="submit" class="btn btn-primary" ng-click="evaluateposttest(3)"            ng-show="!testpassed">     submit questions</button> </form> 

here's plunkr shows dynamic code , demonstrates form never turning valid when radio button in each group selected.

http://plnkr.co/edit/hqgpiocdn3tgle96cpk5?p=preview

and here's plunkr using static content displaying working.

http://plnkr.co/edit/zft2vnbfaqjuu73kanqj?p=preview

just add in javascript controller

$scope.q = [undefined,undefined,undefined,undefined,undefined,undefined]; 

explanation : set ng-model q[question.id] q undefined ng-model won't ever work. must initialize variable in controller. case works not initialize when : ng-model="test"

if

ng-model="test.test" ng-model="test[0]" 

it won't ever work if it's not initialized properly.