LINQ - DistinctBy

demo.cs

var query = people.DistinctBy(p => p.Id);
var query = people.DistinctBy(p => new { p.Id, p.Name });

ext.cs

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;
        }
    }
}