what I should of done

shame.js

var endorsements = [
  {skill:"javascript", user:'billy'},
  {skill:"javascript", user:'bob'},
  {skill:"css",        user:'timmy'},
  {skill:"html",       user:'billy'},
  {skill:"css",        user:'joan'},
  {skill:"css",        user:'fred'},
  {skill:"html",       user:'dubs'}
];

// result
// [
//   {skill:"javascript", users:['billy', 'bob'], count:2},
//   {skill:"css", users:['timmy', 'joan', 'fred'], count:3},
//   {skill:"html", users:['billy', 'dubs'], count:4}
// ]


function parse(data) {
  var obj = createObj(data);
  var ans = [];
  for(var key in obj) {
    var tmpObj = {'skill':key,'users':obj[key],'count':obj[key].length};
    ans.push(tmpObj);
  }
  return ans;
}

function createObj(data) {
  return data.reduce(function(rtnObj,entry) {
    rtnObj[entry.skill] ? rtnObj[entry.skill].push(entry.user) : rtnObj[entry.skill] = [entry.user]
    return rtnObj;
  }, {});
}

console.log(parse(endorsements));