NSIndexPathの配列をソートする

        var indexPathArray=[NSIndexPath(forItem: 2, inSection: 3),NSIndexPath(forItem: 1, inSection: 3),NSIndexPath(forItem: 3, inSection: 1)]

        var indexPathMutableArray=NSMutableArray(array: indexPathArray)
        indexPathMutableArray.sortUsingComparator( { (_a, _b) -> NSComparisonResult in
            let a: NSIndexPath = _a as! NSIndexPath
            let b: NSIndexPath = _b as! NSIndexPath
            return a.compare(b)
        })

NSMutableArray.sortUsingComparatorなら、引数の関数は返り値がNSComparisonResultなので、 NSIndexPath.compare(NSIndexPath)がそのまま使える

【参考】
http://qiita.com/imk2o/items/50de7dbb7dd4fd07f19f
http://stackoverflow.com/questions/14928793/sorting-an-array-of-nsindexpaths