Sorting with multiple row grouped

Initial condition:
--------------
Group Member
D D1
D2
A A1
A2
A3
B B1
--------------

Objective:
--------------
Group Member
A A1
A2
A3
B B1
D D1
D2
--------------

Procedure:
Empty cells on key column must be filled in...
--------------
Group Member
D D1
D D2
A A1
A A2
A A3
B B1
--------------
...then do the sorting and restore empty cells afterward

Here's how to quickly fill in the blanks:
1) Select 'Group' column and press F5>Special>Blanks>OK
2) In active blank cell enter an = sign then point to the cell above and CTRL +
ENTER to fill down
3) Copy>Paste Special(in place)>Values>OK>Esc to get rid of formulas
Source:
How do I group multiple lines of excel info for easy sorting
www.pcreview.co.uk/forums/thread-2334910.php