.

qwen/nodejs/node_modules/lodash/sumBy.js

@@ -0,0 +1,33 @@
+var baseIteratee = require('./_baseIteratee'),
+    baseSum = require('./_baseSum');
+
+/**
+ * This method is like `_.sum` except that it accepts `iteratee` which is
+ * invoked for each element in `array` to generate the value to be summed.
+ * The iteratee is invoked with one argument: (value).
+ *
+ * @static
+ * @memberOf _
+ * @since 4.0.0
+ * @category Math
+ * @param {Array} array The array to iterate over.
+ * @param {Function} [iteratee=_.identity] The iteratee invoked per element.
+ * @returns {number} Returns the sum.
+ * @example
+ *
+ * var objects = [{ 'n': 4 }, { 'n': 2 }, { 'n': 8 }, { 'n': 6 }];
+ *
+ * _.sumBy(objects, function(o) { return o.n; });
+ * // => 20
+ *
+ * // The `_.property` iteratee shorthand.
+ * _.sumBy(objects, 'n');
+ * // => 20
+ */
+function sumBy(array, iteratee) {
+  return (array && array.length)
+    ? baseSum(array, baseIteratee(iteratee, 2))
+    : 0;
+}
+
+module.exports = sumBy;