$scope.array1 = [' ',' ',1,2,3,4,5];
$scope.array2 = [6,7,8,9,10,' ',' '];
$scope.array3 = [12,13,14,15,16,17];

<div ng-repeat="a1 in array1">
    {{a1}}
</div>

<div ng-repeat="a2 in array2">
    {{a2}}
</div>

<div ng-repeat="a3 in array1">
    {{a3}}
</div>

<div ng-repeat="a1 in array1 track by $index">
    {{a1}}
</div>

<div ng-repeat="a2 in array2 track by $index ">
    {{a2}}
</div>

<div ng-repeat="a3 in array1 track by $index">
    {{a3}}
</div>