有效地对IList <T>进行排序而不复制源列表

Question

鉴于下面的测试用例我怎么能:

1. 排序IList<TestObject>基于匹配的索引Id 中的IList<int>列表.
2. 不匹配的值将移动到列表的末尾,并按其原始索引进行排序.在这种情况下,由于索引列表中不存在3和4,我们希望看到list[3] == 3和list[4] == 4.
3. 虽然我知道这可以通过linq实现,但我需要求助于原始列表而不是创建一个新列表(由于列表的存储方式).
4. 源列表必须是IList(我不能使用List<T>)

这是测试:

    public class TestObject
    {
        public int Id { get; set; }
    }

    [Test]
    public void Can_reorder_using_index_list()
    {
        IList<TestObject> list = new List<TestObject>
        {
            new TestObject { Id = 1 },
            new TestObject { Id = 2 },
            new TestObject { Id = 3 },
            new TestObject { Id = 4 },
            new TestObject { Id = 5 }
        };

        IList<int> indexList = new[] { 10, 5, 1, 9, 2 };

        // TODO sort

        Assert.That(list[0].Id, Is.EqualTo(5));
        Assert.That(list[1].Id, Is.EqualTo(1));
        Assert.That(list[2].Id, Is.EqualTo(2));
        Assert.That(list[3].Id, Is.EqualTo(3));
        Assert.That(list[4].Id, Is.EqualTo(4));
    }

更新:

根据要求,这是我尝试过的,但1)它只适用于List<T>和2)我不确定它是最有效的方式:

       var clone = list.ToList();
        list.Sort((x, y) =>
        {
            var xIndex = indexList.IndexOf(x.Id);
            var yIndex = indexList.IndexOf(y.Id);

            if (xIndex == -1)
            {
                xIndex = list.Count + clone.IndexOf(x);
            }
            if (yIndex == -1)
            {
                yIndex = list.Count + clone.IndexOf(y);
            }

            return xIndex.CompareTo(yIndex);
        });

更新2:

感谢@leppie,@ jamiec,@ mitch wheat - 这是工作代码:

    public class TestObjectComparer : Comparer<TestObject>
    {
        private readonly IList<int> indexList;
        private readonly Func<TestObject, int> currentIndexFunc;
        private readonly int listCount;

        public TestObjectComparer(IList<int> indexList, Func<TestObject, int> currentIndexFunc, int listCount)
        {
            this.indexList = indexList;
            this.currentIndexFunc = currentIndexFunc;
            this.listCount = listCount;
        }

        public override int Compare(TestObject x, TestObject y)
        {
            var xIndex = indexList.IndexOf(x.Id);
            var yIndex = indexList.IndexOf(y.Id);

            if (xIndex == -1)
            {
                xIndex = listCount + currentIndexFunc(x);
            }
            if (yIndex == -1)
            {
                yIndex = listCount + currentIndexFunc(y);
            }

            return xIndex.CompareTo(yIndex);
        }
    }

    [Test]
    public void Can_reorder_using_index_list()
    {
        IList<TestObject> list = new List<TestObject>
        {
            new TestObject { Id = 1 },
            new TestObject { Id = 2 },
            new TestObject { Id = 3 },
            new TestObject { Id = 4 },
            new TestObject { Id = 5 }
        };

        IList<int> indexList = new[] { 10, 5, 1, 9, 2, 4 };

        ArrayList.Adapter((IList)list).Sort(new TestObjectComparer(indexList, x => list.IndexOf(x), list.Count));

        Assert.That(list[0].Id, Is.EqualTo(5));
        Assert.That(list[1].Id, Is.EqualTo(1));
        Assert.That(list[2].Id, Is.EqualTo(2));
        Assert.That(list[3].Id, Is.EqualTo(3));
        Assert.That(list[4].Id, Is.EqualTo(4));
    }

Answer 1

已经研究了一会儿，确实如前所述，您将需要ArrayList.Adapter，但是您会注意到它需要一个非通用 IList，因此需要进行一些转换：

ArrayList.Adapter((IList)list)

您还需要编写一个比较器，其中将包含进行排序的逻辑。请原谅这个名字，但是：

public class WeirdComparer : IComparer,IComparer<TestObject>
{
    private IList<int> order;
    public WeirdComparer(IList<int> order)
    {
        this.order = order;
    }
    public int Compare(object x, object y)
    {
        return Compare((TestObject) x, (TestObject) y);
    }

    public int Compare(TestObject x, TestObject y)
    {
        if(order.Contains(x.Id))
        {
            if(order.Contains(y.Id))
            {
                return order.IndexOf(x.Id).CompareTo(order.IndexOf(y.Id));    
            }
            return -1;
        }
        else
        {
            if (order.Contains(y.Id))
            {
                return 1;
            }
            return x.Id.CompareTo(y.Id);
        }
    }
}

编辑：添加了上面的comparerr的实现

那么用法如下：

IList<int> indexList = new[] { 10, 5, 1, 9, 2 };
ArrayList.Adapter((IList)list).Sort(new WeirdComparer(indexList));

顺便说一句，该线程解释了一种将其转换为扩展方法的好方法，这将使您的代码更具可重用性并且更易于阅读（IMO）。