Apple Numbers '09 - Manual (Page 77)

Chapter 3 Using Tables 77
Body rows in the selected range are hidden, but category rows reman visible.
To expand or collapse all category or subcategories of the same level, choose Expand
m
All or Collapse All from the cell reference pop-up menu of any row at the same level
that you want to expand or collapse.
To expand or collapse all categories and subcategories of all levels, hold down the
m
Option key as you click the disclosure triangle near the left edge of any category row.
If one or more categories at the same level are collapsed, then Option-clicking will expand
all categories.
If one of more categories at the same level are expanded, then Option-clicking will
collapse all categories.