linq-从n个列表中返回常见项目 [英] linq - return common items from n number of lists

问题描述

我正在为我们的Intranet应用程序编写一个简单的搜索页面.当用户搜索n个单词时，我会创建n个匹配列表，然后只返回所有列表共有的结果.

I'm writing a simple search page for our intranet application. When a user searches for n words I create n lists of hits and then want to return only the results that are common to all lists.

我正在使用List<int>进行某些操作:

I have something working using List<int> thus:

var list1 = new List<int> {1,2,3,4,5,8,10};
var list2 = new List<int> {3,5,6,9,10,11};
var list3 = new List<int> {3,4,5,10};

var listOfLists = new List<List<int>>{list1,list2,list3};

var results = listOfLists.Aggregate((prevList, nextList) => prevList
                 .Intersect(nextList)
                 .ToList()); 

results.Dump(); //correctly returns 3,5,10, which are common to all lists

但是，如果我在SearchResults类中尝试使用此方法，则不会获得任何结果.这是代码:

However if I try this with my SearchResults class I get no results. Here's the code:

//results from first search word "howard"
List<SearchResult> list1 = new List<SearchResult>();
list1.Add(new SearchResult ("a.html","howard kent"));
list1.Add(new SearchResult ("b.html","howard shaw")); //the common item
list1.Add(new SearchResult ("c.html","howard smith"));
list1.Add(new SearchResult ("d.html","howard moore"));

//results from second search word "shaw"
List<SearchResult> list2 = new List<SearchResult>();
list2.Add(new SearchResult ("e.html","jon shaw"));
list2.Add(new SearchResult ("b.html","howard shaw")); //the common item
list2.Add(new SearchResult ("f.html","chris shaw"));

//could be n further lists...

//make a list of lists
List<List<SearchResult>> searchLists = new List<List<SearchResult>>();
searchLists.Add(list1);
searchLists.Add(list2);

//find results that are common to all lists.
//Doesn't work - returns nil items, should return 1
var results = searchLists
             .Aggregate((prevList, nextList) => prevList
             .Intersect(nextList)
             .ToList()); 

results.Dump();

}

class SearchResult
{
    public string Url{get;set;}
    public string SearchText { get; set; }

//constructor
public SearchResult(string url,string searchText)
{
    Url = url;
 SearchText = searchText;
}

如何更改查询以返回所需的结果?

How should I change the query to return the result I want?

推荐答案

这是因为尽管SearchResult对象具有相同的数据，但它们不是相同的对象.您可以通过实现IEquatable<T>接口来解决此问题. http://msdn.microsoft.com/zh- us/library/ms131187(v = vs.110).aspx

That's because the SearchResult objects are not the same objects, although they have the same data. You can fix this by implementing the IEquatable<T> interface. http://msdn.microsoft.com/en-us/library/ms131187(v=vs.110).aspx

即.

public class SearchResult : IEquatable<SearchResult>
{
    public string Url{get;set;}
    public string SearchText { get; set; }
    public bool Equals(SearchResult other)
    {
        if (other == null)
            return false;
        return string.Concat(this.Url, this.SearchText).Equals(string.Concat(other.Url, other.SearchText), StringComparison.OrdinalIgnoreCase);
    }
}

另一种解决方案是实现IEqualityComparer<T>并将其传递给Enumerable.Intersect方法.

Another solution would be to implement a IEqualityComparer<T> and pass it on to the Enumerable.Intersect method.

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