df.dropNulls { city }.pivotCounts(inward = false) { city }

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: DataFrame: rowsCount = 6, 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
Charlie	Byrd	30	Moscow	90	true

Output DataFrame: rowsCount = 6, columnsCount = 9

name		age	weight	isHappy	London	Dubai	Moscow	Milan	Tokyo
firstName	lastName
Alice	Cooper	15	54	true	1	0	0	0	0
Bob	Dylan	45	87	true	0	1	0	0	0
Charlie	Daniels	20	null	false	0	0	1	0	0
Charlie	Chaplin	40	null	true	0	0	0	1	0
Bob	Marley	30	68	true	0	0	0	0	1
Charlie	Byrd	30	90	true	0	0	1	0	0

pivoted.gather { "London".."Tokyo" }.into("city", "population")

Input DataFrame: rowsCount = 6, columnsCount = 9

name		age	weight	isHappy	London	Dubai	Moscow	Milan	Tokyo
firstName	lastName
Alice	Cooper	15	54	true	1	0	0	0	0
Bob	Dylan	45	87	true	0	1	0	0	0
Charlie	Daniels	20	null	false	0	0	1	0	0
Charlie	Chaplin	40	null	true	0	0	0	1	0
Bob	Marley	30	68	true	0	0	0	0	1
Charlie	Byrd	30	90	true	0	0	1	0	0

Step 1: Gather

name		age	weight	isHappy	key	value
firstName	lastName
Alice	Cooper	15	54	true	London	1
Alice	Cooper	15	54	true	Dubai	0
Alice	Cooper	15	54	true	Moscow	0
Alice	Cooper	15	54	true	Milan	0
Alice	Cooper	15	54	true	Tokyo	0
Bob	Dylan	45	87	true	London	0
Bob	Dylan	45	87	true	Dubai	1
Bob	Dylan	45	87	true	Moscow	0
Bob	Dylan	45	87	true	Milan	0
Bob	Dylan	45	87	true	Tokyo	0
Charlie	Daniels	20	null	false	London	0
Charlie	Daniels	20	null	false	Dubai	0
Charlie	Daniels	20	null	false	Moscow	1
Charlie	Daniels	20	null	false	Milan	0
Charlie	Daniels	20	null	false	Tokyo	0
Charlie	Chaplin	40	null	true	London	0
Charlie	Chaplin	40	null	true	Dubai	0
Charlie	Chaplin	40	null	true	Moscow	0
Charlie	Chaplin	40	null	true	Milan	1
Charlie	Chaplin	40	null	true	Tokyo	0

... showing only top 20 of 30 rows

Output DataFrame: rowsCount = 30, columnsCount = 6

name		age	weight	isHappy	city	population
firstName	lastName
Alice	Cooper	15	54	true	London	1
Alice	Cooper	15	54	true	Dubai	0
Alice	Cooper	15	54	true	Moscow	0
Alice	Cooper	15	54	true	Milan	0
Alice	Cooper	15	54	true	Tokyo	0
Bob	Dylan	45	87	true	London	0
Bob	Dylan	45	87	true	Dubai	1
Bob	Dylan	45	87	true	Moscow	0
Bob	Dylan	45	87	true	Milan	0
Bob	Dylan	45	87	true	Tokyo	0
Charlie	Daniels	20	null	false	London	0
Charlie	Daniels	20	null	false	Dubai	0
Charlie	Daniels	20	null	false	Moscow	1
Charlie	Daniels	20	null	false	Milan	0
Charlie	Daniels	20	null	false	Tokyo	0
Charlie	Chaplin	40	null	true	London	0
Charlie	Chaplin	40	null	true	Dubai	0
Charlie	Chaplin	40	null	true	Moscow	0
Charlie	Chaplin	40	null	true	Milan	1
Charlie	Chaplin	40	null	true	Tokyo	0

... showing only top 20 of 30 rows