LINQ - Full Outer Join

Question

I have a list of people\'s ID and their first name, and a list of people\'s ID and their surname. Some people don\'t have a first name and some don\'t have a surname; I\'d l

Answer 1

My clean solution for situation that key is unique in both enumerables:

 private static IEnumerable FullOuterJoin(
            IEnumerable a, IEnumerable b,
            Func key_a, Func key_b,
            Func selector)
        {
            var alookup = a.ToLookup(key_a);
            var blookup = b.ToLookup(key_b);
            var keys = new HashSet(alookup.Select(p => p.Key));
            keys.UnionWith(blookup.Select(p => p.Key));
            return keys.Select(key => selector(alookup[key].FirstOrDefault(), blookup[key].FirstOrDefault()));
        }

so

    var ax = new[] {
        new { id = 1, first_name = "ali" },
        new { id = 2, first_name = "mohammad" } };
    var bx = new[] {
        new { id = 1, last_name = "rezaei" },
        new { id = 3, last_name = "kazemi" } };

    var list = FullOuterJoin(ax, bx, a => a.id, b => b.id, (a, b) => "f: " + a?.first_name + " l: " + b?.last_name).ToArray();

outputs:

f: ali l: rezaei
f: mohammad l:
f:  l: kazemi