当我不知道创建时的最大大小时，如何使用 Lucene 的 PriorityQueue? [英] How can I use Lucene's PriorityQueue when I don't know the max size at create time?

问题描述

我为 Lucene.Net 构建了一个自定义收集器，但我不知道如何对结果进行排序(或分页).每次调用 Collect 时，我都可以将结果添加到内部 PriorityQueue 中，我知道这是正确的方法.

I built a custom collector for Lucene.Net, but I can't figure out how to order (or page) the results. Everytime Collect gets called, I can add the result to an internal PriorityQueue, which I understand is the correct way to do this.

我扩展了 PriorityQueue，但它在创建时需要一个大小参数.您必须在构造函数中调用 Initialize 并传入最大大小.

I extended the PriorityQueue, but it requires a size parameter on creation. You have to call Initialize in the constructor and pass in the max size.

但是，在收集器中，搜索器只是在获得新结果时调用 Collect，所以 我不知道创建 PriorityQueue 时有多少结果.基于此，我无法弄清楚如何使 PriorityQueue 工作.

However, in a collector, the searcher just calls Collect when it gets a new result, so I don't know how many results I have when I create the PriorityQueue. Based on this, I can't figure out how to make the PriorityQueue work.

我意识到我可能在这里遗漏了一些简单的东西......

I realize I'm probably missing something simple here...

推荐答案

PriorityQueue 不是 SortedList 或 SortedDictionary.这是一种排序实现，它返回 N 个元素的前 M 个结果(您的 PriorityQueue 的大小).您可以使用 InsertWithOverflow 添加任意数量的项目，但它只会包含前 M 个元素.

PriorityQueue is not SortedList or SortedDictionary. It is a kind of sorting implementation where it returns the top M results(your PriorityQueue's size) of N elements. You can add with InsertWithOverflow as many items as you want, but it will only hold only the top M elements.

假设您的搜索产生了 1000000 次点击.您会将所有结果返回给用户吗?更好的方法是将前 10 个元素返回给用户(使用 PriorityQueue(10))和如果用户请求下一个 10 个结果，您可以使用 PriorityQueue(20) 进行新搜索，然后返回下一个 10 元素，依此类推.这是大多数搜索引擎(如 google)使用的技巧.

Suppose your search resulted in 1000000 hits. Would you return all of the results to user? A better way would be to return the top 10 elements to the user(using PriorityQueue(10)) and if the user requests for the next 10 result, you can make a new search with PriorityQueue(20) and return the next 10 elements and so on. This is the trick most search engines like google uses.

每次调用 Commit 时，我都可以将结果添加到内部 PriorityQueue.

我无法理解Commit和search之间的关系，因此我将附上PriorityQueue的示例用法:

I can not undestand the relationship between Commit and search, Therefore I will append a sample usage of PriorityQueue:

public class CustomQueue : Lucene.Net.Util.PriorityQueue<Document>
{
    public CustomQueue(int maxSize): base()
    {
        Initialize(maxSize);
    }

    public override bool LessThan(Document a, Document b)
    {
        //a.GetField("field1")
        //b.GetField("field2");
        return  //compare a & b
    }
}

public class MyCollector : Lucene.Net.Search.Collector
{
    CustomQueue _queue = null;
    IndexReader _currentReader;

    public MyCollector(int maxSize)
    {
        _queue = new CustomQueue(maxSize);
    }

    public override bool AcceptsDocsOutOfOrder()
    {
        return true;
    }

    public override void Collect(int doc)
    {
        _queue.InsertWithOverflow(_currentReader.Document(doc));
    }

    public override void SetNextReader(IndexReader reader, int docBase)
    {
        _currentReader = reader;
    }

    public override void SetScorer(Scorer scorer)
    {
    }
}

<小时>

searcher.Search(query,new MyCollector(10)) //First page.
searcher.Search(query,new MyCollector(20)) //2nd page.
searcher.Search(query,new MyCollector(30)) //3rd page.

编辑@nokturnal

public class MyPriorityQueue<TObj, TComp> : Lucene.Net.Util.PriorityQueue<TObj>
                                where TComp : IComparable<TComp>
{
    Func<TObj, TComp> _KeySelector;

    public MyPriorityQueue(int size, Func<TObj, TComp> keySelector) : base()
    {
        _KeySelector = keySelector;
        Initialize(size);
    }

    public override bool LessThan(TObj a, TObj b)
    {
        return _KeySelector(a).CompareTo(_KeySelector(b)) < 0;
    }

    public IEnumerable<TObj> Items
    {
        get
        {
            int size = Size();
            for (int i = 0; i < size; i++)
                yield return Pop();
        }
    }
}

<小时>

var pq = new MyPriorityQueue<Document, string>(3, doc => doc.GetField("SomeField").StringValue);
foreach (var item in pq.Items)
{
}

这篇关于当我不知道创建时的最大大小时，如何使用 Lucene 的 PriorityQueue?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！