jquery selecting all elements except the last per group

Answer 1

Use this:

$('tr td:not(:last-child)').css('background-color', 'red');

It's saying each <td> that's not the last in that particular <tr>

Answer 2

$('tr').find('td:not(:last)').css('background-color', 'red');

Translates to: for each element in $('tr') selector, do a find() for all tds that are not last.
New result is about tds now, so you can apply .css() as wanted.