public class Comparer<T> : IEqualityComparer<T>
    {
        private readonly Func<T, T, bool> _equalityComparer;
        public Comparer(Func<T, T, bool> equalityComparer)
        {
            _equalityComparer = equalityComparer;
        }
        public bool Equals(T first, T second)
        {
            return _equalityComparer(first, second);
        }
        public int GetHashCode(T value)
        {
            return value.GetHashCode();
        }
    }

new Comparer<DmEmployeeGroup>((x, y) => x.Id == y.Id)