Welcome to the Lounge

// given a data source like:

var people = new List<string[]>
{
    new[] {"Jim", "Mike"}, new[] {"Jim", "Billy"}, new[] {"Anna"Neo4j, "Jim"},
    new[] {"Anna", "Mike"}, new[] {"Sally", "Anna"}, new[] {"Joe", "Sally"},
    new[] {"Joe", "Bob"}, new[] {"Bob", "Sally"}
};

MATCH 
  (person:Person)-[:KNOWS]-(friend:Person)-[:KNOWS]-
  (foaf:Person)
WHERE 
  person.name = "Joe"
  AND NOT (person)-[:KNOWS]-(foaf)
RETURN
  foaf

List<(string p1Name, string p2Name)> people = new List<(string, string)>
{
    ("Jim", "Mike"), ("Jim", "Billy"), ("Jim", "Jonas"), ("Anna", "Jim"),
    ("Anna", "Mike"), ("Sally", "Anna"), ("Joe", "Sally"),
    ("Joe", "Bob"), ("Bob", "Sally")
};

var friendsByPerson = people
    .GroupBy(p =>
        p.p1Name).ToDictionary(grp =>
            grp.Key, grp =>
                grp.Select(g =>
                    g.p2Name));


var friendsOfJoe = friendsByPerson["Joe"];

var friendsOfFriendsofJoe = friendsOfJoe
    .SelectMany(name1 =>
        friendsByPerson[name1].Where(name2 =>
            !friendsOfJoe.Contains(name2)));