df.select { colsAtAnyDepth().filter { !it.isColumnGroup() }.take(3) }

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

Output DataFrame: rowsCount = 7, columnsCount = 3

firstName	lastName	age
Alice	Cooper	15
Bob	Dylan	45
Charlie	Daniels	20
Charlie	Chaplin	40
Bob	Marley	30
Alice	Wolf	20
Charlie	Byrd	30

df.select { colsAtAnyDepth().filter { !it.isColumnGroup() }.takeLast(3) }

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

Output DataFrame: rowsCount = 7, columnsCount = 3

city	weight	isHappy
London	54	true
Dubai	87	true
Moscow	null	false
Milan	null	true
Tokyo	68	true
null	55	false
Moscow	90	true

df.select { colsAtAnyDepth().filter { !it.isColumnGroup() }.drop(3) }

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

Output DataFrame: rowsCount = 7, columnsCount = 3

city	weight	isHappy
London	54	true
Dubai	87	true
Moscow	null	false
Milan	null	true
Tokyo	68	true
null	55	false
Moscow	90	true

df.select { colsAtAnyDepth().filter { !it.isColumnGroup() }.dropLast(3) }

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

Output DataFrame: rowsCount = 7, columnsCount = 3

firstName	lastName	age
Alice	Cooper	15
Bob	Dylan	45
Charlie	Daniels	20
Charlie	Chaplin	40
Bob	Marley	30
Alice	Wolf	20
Charlie	Byrd	30

df.select { colsAtAnyDepth().filter { !it.isColumnGroup() && it.name().startsWith("year") } }

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

Output DataFrame: rowsCount = 0, columnsCount = 0

df.select { colsAtAnyDepth().filter { !it.isColumnGroup() }.except { age } }

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

Output DataFrame: rowsCount = 7, columnsCount = 5

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

df.select { (colsOf<Int>() and age).distinct() }

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

Output DataFrame: rowsCount = 7, columnsCount = 1

age
15
45
20
40
30
20
30