mladenb

public static IEnumerable<TFirst> ExceptBy<TFirst, TSecond>(this IEnumerable<TFirst> first, Func<TFirst, TSecond> mappingFunc, IEnumerable<TSecond> second)
{
	if (first == null) throw new ArgumentNullException(nameof(first));
	if (second == null) throw new ArgumentNullException(nameof(second));

	return ExceptByIterator(first, mappingFunc, second, null);
}

public static IEnumerable<TFirst> ExceptBy<TFirst, TSecond>(this IEnumerable<TFirst> first, Func<TFirst, TSecond> mappingFunc, IEnumerable<TSecond> second, IEqualityComparer<TSecond> comparer)
{