ArrayEnumerable.groupBy Method
        
 Groups elements of this sequence according to a specified key selector function.
 
         
        Parameters
        
            - keySelector
            
 
            - 
                
Type: Function 
            - equalityComparer
            
 
            - 
                
Type: IEqualityComparer
Optional: True 
        
        Return Value
        
Type: IEnumerable
        
ElementType: Grouping
        
An array of groupings.