Excel index match

Skill cxcscmu/SkillLearnBench/skills/b4-skill-creator-claude-opus-4-6/weighted-gdp-calculation/excel-index-match

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npx -y skills add cxcscmu/SkillLearnBench --skill excel-index-match

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How to use INDEX&MATCH for two-dimensional lookups in Excel via openpyxl. Use this skill whenever building Excel formulas that look up values by matching both a row criterion and a column criterion from a data table — e.g., matching a series code (row) and a year (column). Trigger when the user mentions VLOOKUP&MATCH, HLOOKUP&MATCH, XLOOKUP&MATCH, INDEX&MATCH, or two-condition lookups.

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INDEX & MATCH Two-Dimensional Lookup in Excel

When to Use

Use INDEX(range, MATCH(...), MATCH(...)) when you need to retrieve a value from a rectangular data range using two criteria — one to identify the row and one to identify the column.

Formula Pattern

=INDEX(data_range, MATCH(row_criterion, row_lookup_range, 0), MATCH(col_criterion, col_lookup_range, 0))

Components

Part	Purpose
`data_range`	The rectangular block of values (e.g., `Data!H21:M40`)
`row_criterion`	The value to match in the row dimension (e.g., a series code in `$D12`)
`row_lookup_range`	A single column containing the row keys (e.g., `Data!$B$21:$B$40`)
`col_criterion`	The value to match in the column dimension (e.g., a year in `H$9`)
`col_lookup_range`	A single row containing the column keys (e.g., `Data!$H$4:$M$4`)
`0`	Exact match

Locking References

Lock the row criterion column with $D12 (absolute column, relative row) so it adjusts when copied down but not across.
Lock the col criterion row with H$9 (relative column, absolute row) so it adjusts when copied across but not down.
Lock lookup ranges with $ on both dimensions since they never move.

Example in openpyxl

from openpyxl import load_workbook

wb = load_workbook('file.xlsx')
ws = wb['Task']

# Fill a grid of lookup cells
for row in range(12, 18):          # rows 12-17
    for col_idx, col_letter in enumerate(['H','I','J','K','L']):
        formula = (
            f"=INDEX(Data!$H$21:$M$40,"
            f"MATCH($D{row},Data!$B$21:$B$40,0),"
            f"MATCH({col_letter}$9,Data!$H$4:$M$4,0))"
        )
        ws[f'{col_letter}{row}'] = formula

wb.save('file.xlsx')

Common Pitfalls

Ensure the data_range, row_lookup_range, and col_lookup_range all span the same rows/columns of the source data.
Use absolute references ($) on ranges that should not shift when the formula is copied.
The third argument 0 in MATCH means exact match — omitting it defaults to approximate match, which requires sorted data.