C#查找两个或多个列表共有的数字 [英] C# find a number common to two or more lists

问题描述

查找两个或两个以上List中都存在的数字列表的语法是什么?当我只需要检查两个列表时，我一直在循环浏览，但是现在我需要做几个...

What is the syntax for finding a list of numbers both present in two or more List? I was looping through when I only needed to check two lists, but now I need to do several... Something like

List<int> commonIds = SELECT id from list1 
                     where list1.contains(id), 
                           list2.contains(id), 
                           list3.contains(id) ... 

推荐答案

查找任意数量的列表的交集

如果要查找列表的 all 中存在的一组数字，则Enumerable.Intersect是这样做的一个好方法.您甚至不必对列表集合进行硬编码，它可以在运行时创建:

Finding the intersection of any number of lists

If you want to find the set of numbers that exist in all of the lists then Enumerable.Intersect is a good way to do so. You don't even have to hardcode the collection of lists, it can be created at runtime:

var lists = new[] { list1, list2, ..., listN }; // dynamically specified

var common = lists.First().AsEnumerable();
foreach (var list in lists.Skip(1))
{
    common = common.Intersect(list);
}

// and now common has the result, e.g.
var listOfCommonEntries = common.ToList();

查找主列表与彼此之间的交集并

如果要查找包含列表1和列表2之间的所有公共数字的集合，则将列表1和列表N之间的所有公共数字合并，则有些不同:

Finding the union of intersections between master list and each other one

If you want to find the set which includes all common numbers between list 1 and list 2, union all common numbers between list 1 and list N, then it's somewhat different:

var common = Enumerable.Empty<int>();
foreach (var list in lists.Skip(1))
{
    common = common.Union(lists.First().Intersect(list));
}

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