Excel weightedAverage function

gistfile1.js

function weightedAverage(v, w) {
  var sum_v = 0;
  var sum_w = 0;
  if(!v || !w){
    return "#ERROR: You need 2 arguments.";
  }
  if (v.length != w.length) {
    return "#ERROR: Incorrect number of values and weights";  
  }
  var i = v.length;
  while(i--) {
    if(isNaN(parseFloat(v[i]))) continue;
    sum_v += parseFloat(v[i]) * parseFloat(w[i]); 
    sum_w += parseFloat(w[i]); 
  }
  
  return sum_v/sum_w;
}​