angularjs radio、checkbox、ng-repeat

radio使用ng-repeat如何默认选中：

html:

<div class="excels">
   <label ng-repeat="y in mytypeData">
      <input type="radio" ng-model="mytype.value" name="myname" ng-value="y.name"/><span ng-bind="y.name"></span>
   </label>
</div>

js:

$scope.mytype = {value: 'excel'};
$scope.mytypeData = [{
    "name": "excel",
    "checked": true
}, {
    "name": "csv",
    "checked": false
}, {
    "name": "json",
    "checked": false
}, {
    "name": "txt",
    "checked": false
}
];
chceckbox使用ng-repeat，可根据标题切换相应内容，并过滤筛选条件
<div class="dataNavUl">
   <div ng-repeat="x in myExportData" ng-class="{'dataChoice':$parent.dataChoice==$index}" ng-click="$parent.dataChoice=$index">
      <span ng-bind="x.name"></span>
   </div>
</div>
<div class="setting_check" ng-repeat="x in myExportData" ng-show="$parent.dataChoice==$index">
   <div class="form-group">
      <label class="control-label" for="checkboxes">必选：</label>
      <div>
         <button class="but1" ng-disabled="true" ng-repeat="k in x.items | filter:{'required':true}">
            <span ng-bind="k.header"></span>
         </button>
      </div>
   </div>
   <div class="form-group">
      <label class="control-label" for="checkboxes">可选：</label>
      <div>
         <button class="but2"  ng-model="k.checked" ng-class="{'checked':k.checked}" ng-repeat="k in x.items | filter:{'required':false}" ng-click="k.checked=!k.checked;">
            <span ng-bind="k.header"></span>
         </button>
      </div>
   </div>
</div>
js1:
$scope.myExportData=data;
js2:
var uploadData = [];
for (var i = 0; i < $scope.myExportData.length; i++) {
    for (var j = 0; j < $scope.myExportData[i].items.length; j++) {//每个items[i]是一个ss
        if ($scope.myExportData[i].items[j].checked) {
            uploadData.push($scope.myExportData[i].items[j].name);
        }
        if ($scope.myExportData[i].items[j].required) {
            uploadData.push($scope.myExportData[i].items[j].name);
        }
    }
}