distinct function in linque code example

Example 1: c# distinct array of objects by values

var uniquePersons = persons.GroupBy(p => p.Email)
                           .Select(grp => grp.First())
                           .ToArray();

Example 2: c# distinct comparer multiple properties

public static IEnumerable<TSource> DistinctBy<TSource, TKey>
    (this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
    HashSet<TKey> seenKeys = new HashSet<TKey>();
    foreach (TSource element in source)
    {
        if (seenKeys.Add(keySelector(element)))
        {
            yield return element;
        }
    }
}