Function group

public/javascripts/underscore.js:394–404

(behavior)

  // An internal function used for aggregate "group by" operations.
  var group = function(behavior) {
    return function(obj, iteratee, context) {
      var result = {};
      iteratee = cb(iteratee, context);
      _.each(obj, function(value, index) {
        var key = iteratee(value, index, obj);
        behavior(result, value, key);
      });
      return result;
    };
  };

  // Groups the object's values by a criterion. Pass either a string attribute
  // to group by, or a function that returns the criterion.