C# 两个列表对象之间的 Linq 查询
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Linq query between two list objects
提问by Reno
I have two objects:
我有两个对象：
ObjectA
{
string code;
string country;
}
ObjectB
{
string code;
string otherstuff;
}
And I have List<objectA>and List<ObjectB>and I need to find all objects in List<ObjectB>which contains objectA.Code.
But cannot manage to implement it on LINQ query.
我有List<objectA>并且List<ObjectB>我需要找到所有List<ObjectB>包含objectA.Code. 但是无法在 LINQ 查询上实现它。
采纳答案by JaredPar
It sounds like you are trying to find all instances of ObjectBwhich have a codevalue present in any of the List<ObjectA>values. If so try the following
这听起来像你正在努力寻找的所有实例ObjectB其中有一个code存在于任何的价值List<ObjectA>值。如果是这样，请尝试以下操作
List<ObjectA> listA = ...;
List<ObjectB> listB = ...;
var all = listB.Where(b => listA.Any(a => a.code == b.code));
回答by BrokenGlass
To do this effectively you can first put the codes into a HashSet<string>and then use a Contains()query to check if the B in question has a code that is contained in the hashset:
要有效地做到这一点，您可以首先将代码放入 a 中HashSet<string>，然后使用Contains()查询来检查有问题的 B 是否具有包含在哈希集中的代码：
var codes = new HashSet<string>(listOfAs.Select(x => x.code));
var selectedBs = listOfBs.Where( x=> codes.Contains(x.code));
回答by jeroenh
It sounds like you want to join the list of ObjectA with the list of ObjectB on the codeproperty. This is one way:
听起来您想将 ObjectA 的列表与code属性上的 ObjectB 列表连接起来。这是一种方式：
List<ObjectA> listOfA = ...;
List<ObjectB> listOfB = ...;
var all = from a in listOfA
join b in listOfB on a.code equals b.code
select new {a,b};
The result is a list of anonymous objects, containing 2 properties: a of type ObjectA, b of type ObjectB, with the same code
结果是一个匿名对象列表，包含 2 个属性：a 类型 ObjectA，b 类型 ObjectB，具有相同的 code
回答by Olivier Jacot-Descombes
I would put the codes of the ObjectAlist into a HashSet, otherwise your query would become an O(n2) operation. Like this it is an O(n) operation:
我会将ObjectA列表的代码放入 HashSet 中，否则您的查询将变成 O(n 2) 操作。像这样它是一个 O(n) 操作：
var aList = new List<ObjectA>();
var bList = new List<ObjectB>();
var aCodes = new HashSet<string>(aList.Select(a => a.code));
var result = bList.Where(b => aCodes.Contains(b.code));
