sum.js

var arraySum = require('../internal/arraySum'),
    baseCallback = require('../internal/baseCallback'),
    baseSum = require('../internal/baseSum'),
    isArray = require('../lang/isArray'),
    isIterateeCall = require('../internal/isIterateeCall'),
    toIterable = require('../internal/toIterable');

/**
 * Gets the sum of the values in `collection`.
 *
 * @static
 * @memberOf _
 * @category Math
 * @param {Array|Object|string} collection The collection to iterate over.
 * @param {Function|Object|string} [iteratee] The function invoked per iteration.
 * @param {*} [thisArg] The `this` binding of `iteratee`.
 * @returns {number} Returns the sum.
 * @example
 *
 * _.sum([4, 6]);
 * // => 10
 *
 * _.sum({ 'a': 4, 'b': 6 });
 * // => 10
 *
 * var objects = [
 *   { 'n': 4 },
 *   { 'n': 6 }
 * ];
 *
 * _.sum(objects, function(object) {
 *   return object.n;
 * });
 * // => 10
 *
 * // using the `_.property` callback shorthand
 * _.sum(objects, 'n');
 * // => 10
 */
function sum(collection, iteratee, thisArg) {
  if (thisArg && isIterateeCall(collection, iteratee, thisArg)) {
    iteratee = null;
  }
  var noIteratee = iteratee == null;

  iteratee = noIteratee ? iteratee : baseCallback(iteratee, thisArg, 3);
  return noIteratee
    ? arraySum(isArray(collection) ? collection : toIterable(collection))
    : baseSum(collection, iteratee);
}

module.exports = sum;