<input type="radio" id="id1" data-group="group1">
<input type="radio" id="id2" data-group="group1"><br>
<input type="radio" id="id3" data-group="group2">
<input type="radio" id="id4" data-group="group2"><br>
var el=document.getElementsByTagName('input');
for (i=0; i<=el.length; i++) {
if (el[i].getAttribute('type')=='radio' && el[i].getAttribute('data-group')=='group1') {
el[i].setAttribute('checked', false);
}
}