Linq for 2 collection simultaneously

Question

I have two lists:

List listA1 = GetFirstList();
List listA2 = GetSecondList();

and class A definition

<

Answer 1

You can use this one liner:

List<A> result = listA1.Where((t, i) => t.ModifiedDate != listA2[i].ModifiedDate).ToList();

Answer 2

You could use listA1.Except(listA2, cmp) where cmp is an IComparer. Something like:

void Main()
{
    List<A> listA1 = new List<A> {
       new A { Id=1, ModifiedDate=new DateTime(2016,1,1), Type="A"},
       new A { Id=2, ModifiedDate=new DateTime(2016,1,2), Type="A"},
       new A { Id=3, ModifiedDate=new DateTime(2016,1,3), Type="A"},
       new A { Id=4, ModifiedDate=new DateTime(2016,1,4), Type="A"},
    };
    List<A> listA2 = new List<A> {
       new A { Id=1, ModifiedDate=new DateTime(2016,1,1), Type="A"},
       new A { Id=2, ModifiedDate=new DateTime(2016,1,2), Type="A"},
       new A { Id=3, ModifiedDate=new DateTime(2016,1,3), Type="A"},
       new A { Id=4, ModifiedDate=new DateTime(2016,1,5), Type="A"},
       new A { Id=5, ModifiedDate=new DateTime(2016,1,6), Type="A"},
       new A { Id=6, ModifiedDate=new DateTime(2016,1,7), Type="A"},
    };

    var cmp = new AEqualityComparer();
    var result = listA1.Except(listA2, cmp);

    foreach (var item in result)
    {
        Console.WriteLine("Id:{0}, Date:{1}",item.Id, item.ModifiedDate);
    }
}

public class A
{
    public int Id { get; set; }
    public DateTime ModifiedDate { get; set; }
    public string Type { get; set; }
}

public class AEqualityComparer : IEqualityComparer<A>
{
    public bool Equals(A x, A y)
    {
        return x.Id == y.Id && x.ModifiedDate == y.ModifiedDate;
    }

    public int GetHashCode(A obj)
    {
        return obj.ToString().GetHashCode();
    }
}

Answer 3

You can use Enumerable.Zip to link two sequences by index:

List<A> result = listA1.Zip(listA2, (a1, a2) => new { a1, a2 })
    .Where(x => x.a1.ModifiedDate != x.a2.ModifiedDate)
    .Select(x => x.a1)
    .ToList();

This will work even if both sequences don't implement IList/IList<T>, so the items can't be accessed by index.