v		input view
col		column index or name

Onecol returns a view with a single column. It's a simpler version of {colmap}.

set v [view {A B} def {a b c d e f}]

view $v onecol A

	A
0	a
1	c
2	e

view $v onecol -1

	B
0	b
1	d
2	f