Finding equality in items in two lists of differing types?

Overriding Equals (without overriding GetHashCode() ) is a bad idea, and introduces a lot of complexity Listx. Id == item.Id ); Console. WriteLine(isInSecondList); } If you are doing lots of this, or the lists are long - you may benefit from building a hash-set of the known ids first (again, a C# example - sorry): var ids = new HashSet(list2.

Select(x => x.Id)); foreach (ClassB item in list1) { bool isInSecondList = ids. Contains(item. Id); Console.

WriteLine(isInSecondList); } This has the initial cost of hashing all the data, but may be significantly faster overall.

Overriding Equals (without overriding GetHashCode()) is a bad idea, and introduces a lot of complexity. List doesn't allow you to pass in a custom IEqualityComparer, so IMO you should check it manually (foreach etc). Or in .

NET 3.5, LINQ; I'll give a C# example (VB isn't my strong point): foreach (ClassB item in list1) { bool isInSecondList = list2. Any( x=>x.Id == item. Id ); Console.

WriteLine(isInSecondList); } If you are doing lots of this, or the lists are long - you may benefit from building a hash-set of the known ids first (again, a C# example - sorry): var ids = new HashSet(list2. Select(x => x. Id)); foreach (ClassB item in list1) { bool isInSecondList = ids.

Contains(item.Id); Console. WriteLine(isInSecondList); } This has the initial cost of hashing all the data, but may be significantly faster overall.

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