Count number of table rows between two specific rows with jQuery

Question

<table>
  <tr id="parent_1">
    <td>Parent 1</td>
  </tr>
  <tr class="child">
    <td>Child 1</td>
  </tr>
  <tr class="child">
    <td>Child 2</td>
  </tr>
  ...
  <tr id="parent_2">
    <td>Parent2</td>
  </tr>
  ...
</table>

How can I find the number of child rows between parent_1 and parent_2 using jQuery?

Edit: Sorry, didn't make it clear that this is just an example, the table could contain any number of parent rows, and any number of child rows

Answer 1

This will get you what you want

var childCount = ($('#parent_2').get(0).rowIndex - $('#parent_1').get(0).rowIndex) - 1;

Answer 2

This:

$('#parent_1 ~ .child:not(#parent_2 ~ *)').size()

Translation: match all elements of class child that are a sibling of, and come after, #parent_1, but not those that are a sibling of and come after #parent_2.

Answer 3

First idea that came to mind. I'm sure there's some elaborate way to select the elements in question, (meaning you would just have to do $(selector).length) but I can't think of one off the top of my head.

var doCount = false;
var numberOfChildren = 0;

$('tr').each(function(i){
    if($(this).is("#parent_2"))
        doCount = false;

    if(count)
        numberOfChildren++;

    if($(this).is("#parent_1"))
        doCount = true;
});