C# 从另一个中减去一个通用列表
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Subtract a generic list from another
提问by Bobby
I am trying remove a list of firmIDs from one list from another. I don't really understand linq but I am pretty sure I need to use it.
我正在尝试从另一个列表中删除一个公司 ID 列表。我不太了解 linq，但我很确定我需要使用它。
List<Firm> firms = GetBusinessDevelopmentFirms(database);
List<Firm> trackedFirms = GetAllCLIFirmsBeingTrackedByUser();
var result = firms.Contains(i => trackedFirms.Contains(i.FirmID));
The last line doesn't work and the system says "unknown method Contains(?)" even though I have put "using System.Linq;" At the top of the class.
最后一行不起作用，即使我已经输入了“使用 System.Linq;”，系统也会说“未知方法包含（？）” 在班级的顶端。
My idea was to remove a list of tracked firms from a list of all firms to find the untracked firms.
我的想法是从所有公司的列表中删除已跟踪公司的列表，以找到未跟踪的公司。
I hope this makes sense.
我希望这是有道理的。
采纳答案by Alireza
var result = firms.Except(trackedFirms); // returns all the firms except those in trackedFirms
回答by Eli Gassert
Containsis the native method of List<T>that expects you to pass in a T. You want Whereinstead.
Contains是List<T>期望您传入T. 你想要Where。
var result = firms.Where(i => trackedFirms.Contains(i.FirmID));
If you expect resultto be a List<T>then add .ToList()to the end of your WhereLINQ expression.
如果您希望result成为一个List<T>然后添加.ToList()到您的WhereLINQ 表达式的末尾。
回答by Steven Wood
If you have list X and a list Y, and you want to remove all items in Y that are in X you can experiment with the following:
如果您有列表 X 和列表 Y，并且您想删除 Y 中 X 中的所有项目，您可以尝试以下操作：
X.Intersect(Y)
X.相交(Y)
Comparing two Lists and returning the distinct values and the differences
回答by Alessandro D'Andria
I think this should works
我认为这应该有效
var result = firms.Where(x => !trackedFirms.Any(y => x.FirmID == y.FirmID));
From all the firm in firmsselect the firm that isn'tin the trackedFirms(at least this is what i understand from your question).
从各公司firms选择的公司，是不是在trackedFirms（至少这是我从你的问题理解）。
回答by Martin Milan
From your code above, I presume you are trying to get entries from Firms that have a corresponding item in TrackedFirms.
根据您上面的代码，我假设您正试图从在 TrackedFirms 中具有相应项目的公司获取条目。
List<Firm> results = Firms.Where(f => TrackedFirms.Any(t => t.FirmId == f.FirmId)).ToList();
If on the other hand you want untracked firms, then it's :
另一方面，如果您想要未跟踪的公司，那么它是：
List<Firm> results = Firms.Where(f => !TrackedFirms.Any(t => t.FirmId == f.FirmId)).ToList();
回答by Mehmet Taha Meral
The best approach would be Except()for you case. However, if the List object is different then other one, you can use All()
最好的方法是Except()你的情况。但是，如果 List 对象与其他对象不同，则可以使用All()
firms.Where(x=> trackedFirms.All(y => y.FirmId != x.FirmId)
