LINQ Group By Multiple fields -Syntax help

c# linq group-by
Udana picture Udana · Dec 8, 2009 · Viewed 79.3k times · Source

What is the correction needed for example 2 inorder to group by multiple columns

Example 1

var query = from cm in cust
            group cm by new { cm.Customer, cm.OrderDate } into cms
            select
            new 
            { Key1 = cms.Key.Customer,Key2=cms.Key.OrderDate,Count=cms.Count() };

Example 2 (incorrect)

   var qry = 
   cust.GroupBy(p => p.Customer, q => q.OrderDate, (k1, k2, group) =>
   new { Key1 = k1, Key2 = k2, Count = group.Count() });

Answer

Jon Skeet picture Jon Skeet · Dec 8, 2009

Use the same anonymous type in the dot notation that you do in the query expression:

var qry = cust.GroupBy(cm => new { cm.Customer, cm.OrderDate }, 
             (key, group) => new { Key1 = key.Customer, Key2 = key.OrderDate, 
                                   Count = group.Count() });

(In a real IDE I'd have (key, group) lined up under the cm parameter, but then it would wrap in SO.)

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