Summary
	
    Groups the elements of a sequence according to a specified key selector function
    that returns a sequence of keys.
    The keys are compared by using a comparer and each group's elements
    are projected by using a specified function.
    
		
	Syntax
	public static IEnumerable<IGrouping<TKey, TElement>> GroupByMany<TSource, TKey, TElement>(this IEnumerable<TSource> source, Func<TSource, IEnumerable<TKey>> keySelector, Func<TSource, TElement> elementSelector, IEqualityComparer<TKey> comparer)
	Type Parameters
	
		
			
				
					
						| Name | Description | 
				
					
						| TSource | The type of the source. | 
					
						| TKey | The type of the key. | 
					
						| TElement | The type of the element. | 
			
		 
	 	
	Parameters
	
		
			
				
					
						| Name | Type | Description | 
				
					
						| source | IEnumerable<TSource> | The source. | 
					
						| keySelector | Func<TSource, IEnumerable<TKey>> | The key selector. | 
					
						| elementSelector | Func<TSource, TElement> | The element selector. | 
					
						| comparer | IEqualityComparer<TKey> | The comparer. | 
			
		 
	 	
	Return Value
	
		
			
				
					
						| Type | Description | 
				
				
					| IEnumerable<IGrouping<TKey, TElement>> | A sequence of groups. |