Subtract a generic list from another

Question

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.

List firm         


        

Answer 1

The best approach would be Except() for you case. However, if the List object is different then other one, you can use All()

firms.Where(x=> trackedFirms.All(y => y.FirmId != x.FirmId)

Answer 2

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:

X.Intersect(Y)

Comparing two Lists and returning the distinct values and the differences

Answer 3

From your code above, I presume you are trying to get entries from Firms that have a corresponding item in TrackedFirms.

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 :

List<Firm> results = Firms.Where(f => !TrackedFirms.Any(t => t.FirmId == f.FirmId)).ToList();

Answer 4

var result = firms.Except(trackedFirms); // returns all the firms except those in trackedFirms

Answer 5

Contains is the native method of List<T> that expects you to pass in a T. You want Where instead.

var result = firms.Where(i => trackedFirms.Contains(i.FirmID));

If you expect result to be a List<T> then add .ToList() to the end of your Where LINQ expression.

Answer 6

I think this should works

var result = firms.Where(x => !trackedFirms.Any(y => x.FirmID == y.FirmID));

From all the firm in firms select the firm that isn't in the trackedFirms (at least this is what i understand from your question).