■使用例

var arr = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ];
var func = function( val ){
	return val % 2 == 0;
};
// re = [ [2,4,6,8,10], [1,3,5,7,9] ];
var re = _.partition( arr, func );

var obj = [ 
    { 
        title : "Final Fantasy4 Original SoundTrack", 
        year : 1991, 
        author : "Nobuo Uematu"
    }, 
    { 
        title : "Final Fantasy5 Original SoundTrack", 
        year : 1992, 
        author : "Nobuo Uematu"
    }, 
    { 
        title : "Final Fantasy6 Original SoundTrack", 
        year : 1992, 
        author : "Nobuo Uematu"
    },
    { 
        title : "悪魔城ドラキュラX 月下の夜想曲", 
        year : 1994,
        author : "Michiru Yamane"
    } 
];
var func = function( obj ){
	return obj.year == 1992;
}
// re = [[ 
{"title":"Final Fantasy5 Original SoundTrack","year":1992,"author":"Nobuo Uematu"},
{"title":"Final Fantasy6 Original SoundTrack","year":1992,"author":"Nobuo Uematu"}
],[
{"title":"Final Fantasy4 Original SoundTrack","year":1991,"author":"Nobuo Uematu"},
{"title":"悪魔城ドラキュラX 月下の夜想曲","year":1994,"author":"Michiru Yamane"}
]];
var re = _.partition( obj, func );

■内部構造

  _.partition = function(obj, predicate, context) {

// 第3引数が入力されていない、第2引数が関数ならそのまま。
    predicate = cb(predicate, context);
    
    var pass = [], fail = [];
    
// 第1引数「配列（Object）」の各値を第2引数の関数の条件によって振り分ける。
    _.each(obj, function(value, key, obj) {
      (predicate(value, key, obj) ? pass : fail).push(value);
    });
    return [pass, fail];
  };