How to add dynamic value in "data-row-num" by Jquery

I want to add (data-row-num="1",data-row-num="2",data-row-num="3") for my HTML table row.Can someone please help me to do it like ?

<table id="example" class="table table-striped first-table" style="width:100%"><thead><tr><th>Name</th><th>Position</th><th>Office</th></tr></thead><tbody><tr><td>Tiger Nixon</td><td>System Architect</td><td>Edinburgh</td></tr><tr><td>Cedric Kelly</td><td>Senior Javascript Developer</td><td>Edinburgh</td></tr></tbody></table><script type="text/javascript">$(document).ready(function() {   $('#example').dataTable( {  } );});  $("tr").each(function() {    $("tr").attr("data-row-num",????); }); <script>