Question

I have a simple class representing an object. It has 5 properties (a date, 2 decimals, an integer and a string). I have a collection class, derived from CollectionBase, which is a container class for holding multiple objects from my first class.

My question is, I want to remove duplicate objects (e.g. objects that have the same date, same decimals, same integers and same string). Is there a LINQ query I can write to find and remove duplicates? Or find them at the very least?

Answer 1

You can remove duplicates using the Distinct operator.

There are two overloads – one uses the default equality comparer for your type (which for a custom type will call the Equals() method on the type). The second allows you to supply your own equality comparer. They both return a new sequence representing your original set without duplicates. Neither overload actually modifies your initial collection – they both return a new sequence that excludes duplicates..

If you want to just find the duplicates, you can use GroupBy to do so:

var groupsWithDups = list.GroupBy( x => new { A = x.A, B = x.B, ... }, x => x ) 
                         .Where( g => g.Count() > 1 );

To remove duplicates from something like an IList<> you could do:

yourList.RemoveAll( yourList.Except( yourList.Distinct() ) );