In my script I am doing that, but simply concatenating the id from the predefined string "r" and the number of the radio button which is (i) or (j) in my for loops. Like so:
document.getElementById("r" + i)
<input type="radio" id="r11" value=11 DISABLED>Radio 11
In the <input tag> its ID is "r11", so I make the id from specifying the string "r" and the value from the for loop (1 to 15, in this case 11).
Try the script, it does work. ;)