Chapter 7: Why Group?

Linear scanning of large sets is painfully slow. Grouping reduces scan cost dramatically.

Grouping and Hierarchy

Large selection sets are usually organized into layers:

• Items (individual cells)
• Groups (rows, columns, or clusters of items)
• Super-groups (pages or tabs)

This hierarchy reduces scan time and cognitive load. Most systems use a two-level hierarchy, but some allow deeper nesting.

Scan Cost

For N items in linear scan:

• Average cost to select any item = N/2
• Cost to select last item = N

Example: 36 items (6×6)

• Linear average cost: 18 presses
• Row-column average cost: 9 presses

Quick Comparison

Method	Max Presses	Average Presses
Linear (36 items)	36	18
Row‑Column (6×6)	12	9

Hierarchy Visualization

Entire Selection Set (36 items)
        |
  Row1 Row2 Row3 Row4 Row5 Row6
   |    |    |    |    |    |
  6    6    6    6    6    6
items items items items items items