Jquery how to get the index of a row given only certain <tr> s, not all of them

PROBLEM: I want to get the row index of only rows where the "AC" button is. What for? because I need a dynamically added comment to match the index I get in the POST.

Here is my code:

<div class='row'>
<div class='col-xs-12 col-sm-12 col-md-12 col-lg-12'>
<table id="items" class="table table-bordered table-hover">
    <thead>
    <tr>
        <th width="2%"><input id="check_all" class="formcontrol" type="checkbox"/></th>
        <th width="2%">AC</th>
        <th width="15%">Codigo</th>
        <th width="38%">Articulo</th>
        <th width="15%">Precio</th>
        <th width="15%">Cantidad</th>
        <th width="15%">Total</th>

    </tr>
    </thead>
    <tbody>
    <tr>
        <td><input class="case" type="checkbox"/></td>
        <td><button class="btn btn-success addrow" type="button">AC</button></td>
        <td><input type="text" data-type="productCode" name="items[code][]" id="itemNo_1" class="form-control autocomplete_txt" autocomplete="off"></td>
        <td><input type="text" data-type="productName" name="items[name][]" id="itemName_1" class="form-control autocomplete_txt" autocomplete="off"></td>
        <td><input type="number" name="items[price][]" readonly="readonly" id="price_1" class="form-control changesNo" autocomplete="off" onkeypress="return IsNumeric(event);" ondrop="return false;" onpaste="return false;"></td>
        <td><input type="number" name="items[quantity][]" id="quantity_1" class="form-control changesNo" autocomplete="off" onkeypress="return IsNumeric(event);" ondrop="return false;" onpaste="return false;"></td>
        <td><input type="number" name="items[total][]" readonly="readonly" id="total_1" class="form-control totalLinePrice" autocomplete="off" onkeypress="return IsNumeric(event);" ondrop="return false;" onpaste="return false;"></td>

    </tr>
    </tbody>
</table>
</div>
</div>
<div class='row'>
<button class="btn btn-danger delete" type="button">-  eliminar</button>
<button class="btn btn-success addmore" type="button">+ Agregar</button>

    </div>

      

        
        
        
      

    

And here's the script:

var i=$('table tr').length;
$(".addmore").on('click',function(){
html = '<tr>';
html += '<td><input class="case" type="checkbox"/></td>';
html += '<td><button class="btn btn-success addrow" type="button" id="addrow_'+i+'">AC</button></td>';
html += '<td><input type="text" data-type="productCode" name="items[code][]" id="itemNo_'+i+'" class="form-control autocomplete_txt" autocomplete="off"></td>';
html += '<td><input type="text" data-type="productName" name="items[name][]" id="itemName_'+i+'" class="form-control autocomplete_txt" autocomplete="off"></td>';
html += '<td><input type="text"  name="items[price][]" readonly="readonly" id="price_'+i+'" class="form-control changesNo" autocomplete="off" onkeypress="return IsNumeric(event);" ondrop="return false;" onpaste="return false;"></td>';
html += '<td><input type="text"  name="items[quantity][]" id="quantity_'+i+'" class="form-control changesNo" autocomplete="off" onkeypress="return IsNumeric(event);" ondrop="return false;" onpaste="return false;"></td>';
html += '<td><input type="text"  name="items[total][]" readonly="readonly" id="total_'+i+'" class="form-control totalLinePrice" autocomplete="off" onkeypress="return IsNumeric(event);" ondrop="return false;" onpaste="return false;"></td>';
html += '</tr>';
$('#items').append(html);
i++;
});


$(document).on("click", '.addrow', function (){
var count =  $(this).parent().parent().index();
newrow = '<tr><td><input class="case" type="checkbox"/></td><td colspan="7"><input type="text" name="items[comment]['+count+']" class="form-control"></td></tr>';
$(this).parent().parent().after(newrow); 
});

      

        
        
        
      

    

Here is a jsfiddle: https://jsfiddle.net/1ejw1h68/

My problem is here, I believe: var count = $ (this) .parent (). parent (). index ();

If I add new items and "THEN" adds "AC" everything works fine, I get the same indices in my POST request, but if I add an item and then a comment, etc., the indices won't match the comments.

How can I fix this?

Edit: Clarification: When I submit the form, I get a post request with an array of elements, each array has an index that matches the index of the table, my problem is that some elements may or may not have a comment.

It works if I add items and comments in order, if I add 4 items first and then add a comment to the second item, I get this in my POST:

[comment] => Array
            (
                [1] => this is a comment, and it should be index 1
            )

      

        
        
        
      

    

But if I, for example, add an element, then a comment, then a comment, then an element, etc., for the comment of the second element, this is what I get:

[comment] => Array
            (
                [0] => 
                [2] => this is a comment, and it should be index 1
                [4] => 
            )

      

        
        
        
      

    

As you can see, the second time I added comments var count = $ (this) .parent (). parent (). index (); counted comment lines in relation to the total number of indexes, how can I prevent this? or is there a better way to do this?