Implement PERCENTOF function

[Jython1415]

Overview

Implement the PERCENTOF function for the named-functions library.

Description

Sums the values in a subset and divides it by the sum of all values to calculate percentage contribution.

Value Proposition

• Common business calculation for proportion analysis
• Simple but frequently needed in dashboards and reports
• Useful for part-to-whole analysis
• Saves users from writing repetitive formulas

Priority

HIGH

Category

Aggregation & Calculation

Implementation Notes

• Parameters: subset_range, total_range
• Should handle division by zero (when total is 0)
• Consider returning as decimal (0.25) vs percentage (25%) - document clearly
• Should handle non-numeric values gracefully
• Consider variant that takes a condition instead of explicit subset

Related

Part of Excel function implementation initiative (#51)

[Jython1415]

Implemented in #124