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REDUCE Function
Summary
The REDUCE function transforms an array into a single accumulated value by iteratively applying a custom LAMBDA function to each element, starting from an optional initial value. This powerful array processing tool enables complex reductions like conditional sums, products, and custom aggregations.
Syntax
REDUCE([initial_value], array, LAMBDA(accumulator, value, body))Parameters
| Parameter | Type | Required | Description |
|---|---|---|---|
| initial_value | Any |
No | Sets the initial accumulator value; omit to use first array element |
| array | Array |
Yes | Array or range containing values to reduce |
| lambda | LAMBDA |
Yes | Custom LAMBDA function that processes accumulator and current value |
Using the REDUCE Function
REDUCE excels at custom array reductions beyond simple SUM or PRODUCT. Use it for conditional aggregations, custom counting logic, or any iterative calculation requiring accumulated results across array elements.
Common REDUCE Examples
Sum of Squared Values
=REDUCE(, A1:C2, LAMBDA(a,b,a+b^2))Sums the squares of all values in range A1:C2 by accumulating squares (no initial value)
Conditional Product (>50 only)
=REDUCE(1,Table1[nums],LAMBDA(a,b,IF(b>50,a*b,a)))Multiplies only numbers greater than 50, starting with 1 and skipping others
Count Even Numbers
=REDUCE(0,Table2[Nums],LAMBDA(a,n,IF(ISEVEN(n),a+1,a)))Counts even numbers in table by incrementing accumulator only for even values
Frequently Asked Questions
Common Errors and Solutions
#VALUE! - Incorrect Parameters
Cause: Invalid LAMBDA syntax or wrong number of LAMBDA parameters
Solution: Ensure LAMBDA has exactly 3 parameters: accumulator, value, body
#CALC!
Cause: Empty array with omitted initial_value
Solution: Provide initial_value or ensure array has data
Notes
- Perfect companion to LAMBDA for functional programming
- Use 0 for sum/count operations, 1 for product operations
- Processes rows, columns, or 2D arrays
- Combine with BYROW/BYCOL for multi-dimensional reductions
Compatibility
Available in: Excel 365, Excel 2021
Not available in: Excel 2019, Excel 2016, Excel 2013, Excel 2010, Excel 2007
Content last reviewed: December 9, 2025
Update frequency: As needed
Excel versions tested: Excel 365, Excel 2021