c# - How to group a list of lists into repeated items -

i have c# problem. have list of object of type item. need group sub item lists of of these both "subitemcode", can repeated between items, , "subitemgroup", can repeated. have idea i'll want linq grouping, unsure group by?

class item {    string itemcode;    list<subitem> subitems; }  class subitem {   string subitemcode;   string subitemgroup;   list<string> validparentitems; } 

so, idea like

 var results = item in itemlist                subitem in item.subitems                group subitem ??????? 

so, pointer @ how can group items?

note: before says, not homework. don't see point in tearing hair out on when getting on more productive. no point re-inventing wheel right?

try this:

var results = itemlist.selectmany(i => i.subitems).groupby(i => i.subitemgroup);