jQuery set var where n is ID for tabindex order?

jQuery set var where n is ID for tabindex order?

HTML

Name:<input type="text" id="input_1" /><br />
    <input type="hidden" /><br />
    <input type="hidden" /><br />
    Age:
    <input type="text" id="input_3" /><br />
    Birth:
    <input type="text" /><br />
    Test:<select>
        <option>a</option>
        <option>b</option>
    </select><br />
    Gender:
    <input type="radio" name="gender" />
    Male
    <input type="radio" name="gender" />Female
    <br />
    Vechical:
    <input type="checkbox" name="Vechical" /><br />
    <input type="checkbox" name="Vechical" /><br />
    <input type="checkbox" name="Vechical" /><br />
    <input type="hidden" />
    test1:
    <input type="text" id="input_7" /><br />
    test2:
    <input type="text" /><br />
    test3:
    <input type="text" /><br />
    test4:
    <input type="text" /><br />

JavaScript

$(document).ready(function () {
            var tab_order_positions = ['1', '7', '3']
            var tabindex = tab_order_positions.length;

            $.each(tab_order_positions, function (i, tab_order_position) {
                //$('#input_' + tab_order_position).attr('tabindex', i);
            });

            $('input, select').each(function (i) {
                var obj = $(this);

                if (obj.attr('type') != 'hidden' && (obj.attr('id') !== undefined && $.inArray(obj.attr('id').split('_')[1], tab_order_positions)) === false) {
                 //   obj.attr('tabindex', tabindex);
                    tabindex++;
                }
            });
        });