Question

I have two lists of the same type. That type does not have an identifier or any other guaranteed way to programatically distinguish.

• List A: {1, 2, 2, 3, 5, 8, 8, 8}
• List B: {1, 3, 5, 8}

I want the items from A that are not in B.

• Desired Result: {2, 2, 8, 8}

If the types had identifiers, I could use a statement like the following…

var result = listA
      .Where(a => listB.Where(b => b.Id == a.Id).Count() == 0)
      .ToList();

So far, the only way I can do this is with a loop where I add each item the number of times it doesn’t appear in the original list.

foreach (var val in listB.Select(b => b.val).Distinct())
{
  var countA = listA.Where(a => a.val == val).Count();
  var countB = listB.Where(b => b.val == val).Count();
  var item = listA.Where(a => a.val == val).FirstOrDefault();

  for (int i=0; i<countA-countB; i++)
    result.Add(item);
}

Is there a cleaner way to achieve this?

EDIT:
Here is a simplified version of the object in the lists. It’s coming from a Web service that’s hitting another system.

public class myObject
{
  public DateTime SomeDate { get; set; }
  public decimal SomeNumber; { get; set; }
  public bool IsSomething { get; set; }
  public string SomeString { get; set; }
}

The data I am receiving has the same values for SomeDate/SomeString and repeated values for SomeNumber and IsSomething. Two objects might have equal properties, but I need to treat them as distinct objects.

Answer 1

try this:

var listA = new List<Int32> {1, 2, 2, 3, 5, 8, 8, 8};
var listB = new List<Int32> {1, 3, 5, 8};
var listResult = new List<Int32>(listA);

foreach(var itemB in listB)
{
    listResult.Remove(itemB);
}