c# - Find missing information between 2 lists -

how can find missing information between 2 different lists in

the code generates lists

 private static ienumerable<user> getsomeusers()         {             var mikesgroups = new list<string> { "group1", "group2" };             var mike = new user { username = "mike", memberof = mikesgroups };              var davidsgroups = new list<string> { "group3", "group1" };             var david = new user { username = "david", memberof = davidsgroups };              return new list<user> { mike, david };         }           private static ienumerable<group> getgroups()         {             var group1users = new list<string> { "mike", "david", "kim" };             var group1 = new group { name = "group1", members = group1users };              var group2users = new list<string> { "mike", "david","kim" };             var group2 = new group { name = "group2", members = group2users };              return new list<group> { group1, group2 };         } 

entities:

public class user     {        public string username { get; set; }        public ilist<string> memberof { get; set; } // list of group names     }  public class group {    public string name { get; set; }    public ilist<string> members { get; set; } // list of username } 

result should 2 lists (missing groups , missing users)

group3 missing in group list , linked user "david" kim missing in user list , linked group1 , group2

2 dictionaries must returned key = missing value = foundin

dictionary<string,ilist<string>> missingusers; item 1 > key="kim", value={"group1","group2"}  dictionary<string,ilist<string>> missinggroup; item 1 > key="group3",{"david"} 

edit=>

i manged list of missing not linked (list of values in dictionary)

var missinggroups = users.selectmany(g => g.memberof).tolist().except(groups.select(w => w.name)); var missingusers= groups.selectmany(g => g.members).tolist().except(users.select(u => u.username)); 

ok, found solution. please feel free correct if found better 1 has better performance.

        var missinggroup =         users.todictionary(user => user.username, user =>              user.memberof.except(groups.select(w => w.name)))             .where(f => f.value != null && f.value.count() > 0)             .todictionary(x => x.key, x => x.value);