A simple convenience function for adding together an array of numbers.

//
// Iterates over an array of numbers and returns the sum. Example:
//
//   _.sum([1, 2, 3]) => 6
//
_.sum = function(obj) {
  if (!$.isArray(obj) || obj.length == 0) return 0;
  return _.reduce(obj, function(sum, n) {
    return sum += n;
  });
}

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