AngularJS set dynamic key in array input

I am new to AngularJS

And i have trouble to set dynamic key value.

Here is my code,

VIEW

<td>
    <input type="number" class="form-control" ng-model="title[id]" />
</td>

Controller

$scope.update = function() {
    $http({
        url: 'update.php',
        method: "POST",
        data: $scope.title
    }).success(function (data) {});
}

PHP

[amount] => Array
    (
        [0] => 
        [1] => 
        [2] => 
        [3] => 
        [4] => 
        [5] => 
        [6] => 
        [7] => 
        [8] => 
        [9] => 10
        [10] => 
        [11] => 
        [12] => 12
    )

So, my question is if i use id as input array key then always array start with 0 index not specific index.

Thank you !