Dynamic Changing dropdown boxes

Hi All.
I have a javascript function that changes the value of the next dropdown box from a list of multiple dropdown boxes based on an onchange event as shown below.
What I want to do is if the user selects for instance “software manufacturer” then it is never available again in any of the next dropdown boxes.
I can get this to work for the next checkbox but it comes back again for the 3rd checkbox.

Hope it makes sense

var categories = [];
categories["startList"] = ["Software Manufacturer","Product Name","Product Version","Keep Existing","Ignore"]
categories["Software Manufacturer"] = ["Product Name","Product Version","Keep Existing","Ignore"];
categories["Product Name"] = ["Software Manufacturer","Product Version","Keep Existing","Ignore"];
categories["Product Version"] = ["Software Manufacturer","Product Name","Keep Existing","Ignore"];
 categories["Keep Existing"] = ["Software Manufacturer","Product Name","Product Version","Keep Existing","Ignore"];
 categories["Ignore"] = ["Software Manufacturer","Product Name","Product Version","Keep Existing","Ignore"];

almost forgot, here is my fillselect function and i forgot to mention that if a user selects software_manufacturer, product_name or product_version then they would not be available twice, the keep existing and ignore can be repeated for every box

function fillSelect(sel,ary,nxt){
 if (ary&&sel.form){
  var frm=sel.form,nme=sel.name.replace(/\d/g,""),i=Number(sel.name.replace(/\D/g,""))+1,nxt=frm[nxt],z0=0;
  while (frm[nme+i]){
   frm[nme+i].length = 1;
  for (;z0<ary.length;z0++){
   nxt.options[z0+1]=new Option(ary[z0],ary[z0]);

This is a javascript question not php.

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