c# - Best way to use LINQ to fill in gaps in my data -

yesterday posted question below on how use linq transform object several levels using 'group' flat structure:

linq groupby on object several levels

this kindly answered cédric bignon. reason wanted transformation populate componentart's silverlight xychart component userdata variable. however, i've found out there known bug component when displaying in stacked bar format. if there's gaps in data not display properly, need ensure users have value distinct values of category. in original question, i've put i'd userdata populated with, i'd need ensure [user = "bob", category = "international", spend = 0.00] present in results.

i've achieved using following code after linq statement have given me:

// linq statement provided @cedric  var userdata = spend in allspend            userdatapoint in                (from monthspend in spend.spend                spenddetail in monthspend.detail                group spenddetail spenddetail.description g                select new userdatapoint                {                    user = spend.username,                    category = g.key,                    spend = g.sum(t => t.amount)                })            select userdatapoint; // end  list<userdatapoint> userdatanogaps = new list<userdatapoint>(); userdatanogaps = userdata.tolist(); foreach (string strcategory in userdata.select(c => c.category).distinct()) {     var existing = userdata.where(c => c.category == strcategory).select(c => c.user);     userdatanogaps.addrange(userdata.where(c => !existing.contains(c.user)).select(c => new userdatapoint() { user = c.user, category = strcategory, spend = 0 })); } 

but code pretty slow when have on 1000 users , few categories. can somehow incorporated linq statement cédric provided or better off filling in gaps afterwards using code above?

you can prepare list of points users/categories 0 values merge userdata union.

var userdatalist = userdata.tolist();  var userslist = userdatalist.select(x => x.uder).distinct().tolist(); var categorieslist = userdatalist.select(x => x.category).distinct().tolist();     // make list of userdatapoint 0 sums var empty = (from user in users             category in categorieslist              select new userdatapoint                        {                           user = user,                           category = category,                           spend = 0                        }).tolist();       var merged = userdatalist.union(empty)                          .groupby(x => new { x.user, x.category }) // here sum empty points real                          .select(new userdatapoint {                              user = group.key.user,                              category = group.key.category,                              spend = group.sum(y => y.spend)                          }).tolist();