Input DataFrame: rowsCount = 7, columnsCount = 5

name		age	city	weight	isHappy
firstName	lastName
Alice	Cooper	15	London	54	true
Bob	Dylan	45	Dubai	87	true
Charlie	Daniels	20	Moscow	null	false
Charlie	Chaplin	40	Milan	null	true
Bob	Marley	30	Tokyo	68	true
Alice	Wolf	20	null	55	false
Charlie	Byrd	30	Moscow	90	true

Step 1: GroupBy

firstName	group
Alice	DataFrame 2 x 5
Bob	DataFrame 2 x 5
Charlie	DataFrame 3 x 5

Output DataFrame: rowsCount = 3, columnsCount = 4

firstName	mean age	count	total
	city	city
Alice	{ London: 15.0, null: 20.0 }	{ London: 1, null: 1 }	2
Bob	{ Dubai: 45.0, Tokyo: 30.0 }	{ Dubai: 1, Tokyo: 1 }	2
Charlie	{ Moscow: 25.0, Milan: 40.0 }	{ Moscow: 2, Milan: 1 }	3