Left outer join

LinqBegin54.cs

public static void LinqBegin54()
{
     IEnumerable<string> a 
        = new[] {"AA", "B21", "A32", "VS", "S", "AAA"}; 
    IEnumerable<string> b 
        = new[] {"B2", "BSS3", "AD6", "SSS"}; 

    /*
        var result =
        a.GroupJoin(b, x => x[0], x => x[0], 
            (x, y) => y.DefaultIfEmpty("")
                       .Select(z => x + "." + z))
            .SelectMany(x => x)
            .OrderBy(x => x);
    */

    var result =
        from x in a
        join y in b
            on x[0] equals y[0]
            into yy
        from z in yy.DefaultIfEmpty("")
        orderby x, z
        select x + "." + z;
    Console.WriteLine(string.Join(" ", result));
}