Excel index match

Skill cxcscmu/SkillLearnBench/skills/b1-one-shot-claude-opus-4-6/weighted-gdp-calculation/excel-index-match

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Using INDEX/MATCH formulas in Excel for two-condition lookups across sheets.

SKILL.md

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INDEX & MATCH for Two-Condition Lookups in Excel

Pattern: Cross-Sheet Lookup with Two Criteria

When you need to look up a value using both a row identifier and a column identifier (e.g., series code + year), use INDEX/MATCH:

=INDEX(DataRange, MATCH(RowCriteria, RowLookupRange, 0), MATCH(ColCriteria, ColLookupRange, 0))

Example

Given a Data sheet with series codes in column B and years in row 4:

=INDEX(Data!$H$21:$M$40, MATCH($D12, Data!$B$21:$B$40, 0), MATCH(H$9, Data!$H$4:$M$4, 0))

Key Points

Use $ to lock ranges that shouldn't shift when copying formulas
Lock row criteria column with $D12 (column locked, row relative)
Lock year row with H$9 (column relative, row locked)
The third argument 0 means exact match
INDEX range and MATCH ranges must align (same rows/columns)

Openpyxl Implementation

# When writing INDEX/MATCH formulas via openpyxl, use string assignment:
ws['H12'] = '=INDEX(Data!$H$21:$M$40,MATCH($D12,Data!$B$21:$B$40,0),MATCH(H$9,Data!$H$4:$M$4,0))'