Compare the values of properties of two objects in LINQ

Question

I have two lists of Student Object in my code List<student> list1 and List<student> list2. The student object has the following properties. FirstName LastName University

I have the following method where I would like to compare the value of the respective property between the objects in the two list using LINQ. I found a few examples in LINQ that showed how to compare two values in a list of integers or string, but could not find any examples that compares the property value of the objects in the List.

`private CompareList(ref List<student> L1,ref List<student> L2)
 {
   // compare FirstName of L1 to L2
      ......

 }`

How would I go about doing this? Thanks!

Answer 1

public static bool Compare(ref List<Student> list1, ref List<Student> list2)
{
        return Enumerable.SequenceEqual(list1,list2, new MyCustomComparer());
}

public class MyCustomComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.FirstName == y.FirstName && x.LastName == y.LastName && x.University == y.University)
            return true;
        return false;
    }

    public int GetHashCode(Student obj)
    {
        throw new NotImplementedException();
    }
}

Answer 2

You didn't say what exactly you want to check, but if you just want to know if two collections are equal then I guess you could check it this way:

bool isAnyElementFromL1NotInL2 = L1.Select(x => x.Name).Except(L2.Select(y => y.Name)).Any();
bool isAnyElementFromL2NotInL1 = L2.Select(x => x.Name).Except(L1.Select(y => y.Name)).Any();
bool areL1AndL2TheSame = !isAnyElementFromL1NotInL2 && !isAnyElementFromL2NotInL1;

See also this answer by Jon Skeet

Or this question.

Answer 3

The best ways to do it would be to either the student (types are conventionally Pascal cased) being comparable by implementing the IComparable<student>/IStructuralComparable or IEquatable<student>/IStructuralEquatable or by creating a comparer class implementing IComparaer<T>.