Remove items from list 1 not in list 2

Question

I am learning to write lambda expressions, and I need help on how to remove all elements from a list which are not in another list.

var list = new List

        

Answer 1

This question has been marked as answered, but there is a catch. If your list contains an object, rather than a scalar, you need to do a bit more work.

I tried this over and over with Remove() and RemoveAt() and all sorts of things and none of them worked correctly. I couldn't even get a Contains() to work correctly. Never matched anything. I was stumped until I got the suspicion that maybe it could not match up the item correctly.

When I realized this, I refactored the item class to implement IEquatable, and then it started working.

Here is my solution:

class GenericLookupE : IEquatable
{
    public string   ID  { get; set; }

    public bool     Equals( GenericLookupE other )
    {
        if ( this.ID == other.ID )      return true;

        return false;
    }
}

After I did this, the above RemoveAll() answer by Reed Copsey worked perfectly for me.

See: http://msdn.microsoft.com/en-us/library/bhkz42b3.aspx