Select one javascript for radio buttons

I have the javascript below to make sure a user checks at least one checkbox.
Seems to work fine for checkboxes but not for radio buttons. I need help tweaking it so that it works.

I have a repeated region displaying names, they all have ids, I need the user to select one of the radio buttons.

<script language="JavaScript">
function oneCheckboxChecked(form){
for(f=0;f<form.length;f++){
if(form[f].type !="checkbox") continue;
if(form[f].checked){
return true;
}
}
alert("Select at least one User");{
return false;
}
}
</script>

A