@@ -160,6 +160,32 @@ from sample in _sampleList
160160 }
161161 }
162162
163+ private void SumAgeByLastnameAndPlaceGroupingWithLet ( )
164+ {
165+ var ageLastnameGroups =
166+ from sample in _sampleList
167+ group sample by new
168+ {
169+ sample . LastName ,
170+ sample . Place
171+ }
172+ into sampleGroup
173+ let sumAge = sampleGroup . Sum ( x => x . Age )
174+ let memberCount = sampleGroup . Count ( )
175+ select
176+ new
177+ {
178+ GroupingKey = sampleGroup . Key ,
179+ SumAge = sumAge ,
180+ CountMembers = memberCount
181+ } ;
182+ //use result
183+ foreach ( var sample in ageLastnameGroups )
184+ {
185+ Console . WriteLine ( $ "Lastname = { sample . GroupingKey . LastName } , Place = { sample . GroupingKey . Place } , { sample . CountMembers } member(s), SumAge = { sample . SumAge } ") ;
186+ }
187+ }
188+ 163189 private void SumAgeByLastnameAndPlaceGroupingOrdered ( )
164190 {
165191 var ageLastnameGroups =
@@ -283,6 +309,9 @@ public override void Execute()
283309 Section ( "Group by LastName and Place" ) ;
284310 SumAgeByLastnameAndPlaceGrouping ( ) ;
285311 LineBreak ( ) ;
312+ Section ( "Group by LastName and Place (using 'let' keyword)" ) ;
313+ SumAgeByLastnameAndPlaceGroupingWithLet ( ) ;
314+ LineBreak ( ) ;
286315 Section ( "Group by LastName (ordered by member count, desc)" ) ;
287316 SumAgeByLastnameGroupingOrderedDescending ( ) ;
288317 LineBreak ( ) ;
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