Calculating mean

mean.js

function mean(obj)
{
  var props = getProps(obj);
  var means = [];
  function findMean(item){
    var found = -1;
    for (var i = means.length - 1; i >= 0; i--) {
      if(means[i].prop === item){
        found = i;
      }
    }
    return found;
  }
  var frequencies = getFrequency(obj);
  for (var i = frequencies.length - 1; i >= 0; i--) {
    if(typeof frequencies[i].val === 'number'){
      var foundMean = findMean(frequencies[i].prop);
      if(foundMean===-1){
        means.push({prop:frequencies[i].prop,count:frequencies[i].frequency,sum:frequencies[i].val,mean:frequencies[i].val});
      } else {
        means[foundMean].count+=frequencies[i].frequency;
        means[foundMean].sum+=(frequencies[i].val * frequencies[i].frequency);
        means[foundMean].mean = means[foundMean].sum /means[foundMean].count;
      }
    }
  }
  return means;
}
function getFrequency(obj){
  var size = obj.length;
  var items = [];
  var props = getProps(obj);
  function findItem(itemSearched){
    var found = -1;
    for (var i = 0; i<items.length;i++) {
      if(items[i].prop == itemSearched.prop && items[i].val == itemSearched.val)
      {
        found = i;
      }
    }
    return found;
  }
  for(var i = 0; i<props.length;i++)
  {
    for(var j=0; j<size;j++)
    {
      var item = {prop:props[i].prop,val:obj[j][props[i].prop],frequency:1};
      var foundItem = findItem(item);
      if(foundItem ===-1){
        items.push(item);
      } else {
          items[foundItem].frequency+=1
      }
    }
  }
  return items;
}
function getProps(obj){
  var size = obj.length;
  var props = [];
  function findProp(property,type)
  { 
    var found = false;
    props.forEach(function(prop){
      if(prop.prop==property && prop.type==type){
        found = true;
      }
    })
    return found;
  }
  for(var i=0;i<size;i++){
    if(typeof obj[i] === 'object'){
      Object.keys(obj[i]).forEach(function(prop){
        var valueType = typeof obj[i][prop];
        if(!findProp(prop,valueType)){
          props.push({prop:prop,type:valueType});
        }
      });
    }
  }
  return props;
}

//example : 
var ages = [{age:12},{age:13},{age:20},{17}];
console.log(ages);