Summary
	
    Creates a lookup from a sequence of documents and the values of a specified metadata key
    using the value of the specified element metadata for the elements of the lookup
    and compares the keys by using a specified comparer.
    If a document does not contain the specified key or element metadata keys, it is not included in the result set.
    
		
	Syntax
	public static ILookup<TKey, TElement> ToLookup<TKey, TElement>(this IEnumerable<IDocument> documents, string keyMetadataKey, string elementMetadataKey, IEqualityComparer<TKey> comparer)
	Type Parameters
	
		
			
				
					
						| Name | Description | 
				
					
						| TKey | The type of the key. | 
					
						| TElement | The type of the element. | 
			
		 
	 	
	Parameters
	
		
			
				
					
						| Name | Type | Description | 
				
					
						| documents | IEnumerable<IDocument> | The documents. | 
					
						| keyMetadataKey | string | The key metadata key. | 
					
						| elementMetadataKey | string | The element metadata key. | 
					
						| comparer | IEqualityComparer<TKey> | The comparer. | 
			
		 
	 	
	Return Value
	
		
			
				
					
						| Type | Description | 
				
				
					| ILookup<TKey, TElement> | A lookup. |