Syntax
REDUCE(initial_value, array, lambda)
| Parameter | Description |
|---|---|
| initial_value | Parameter of the REDUCE function. |
| array | Parameter of the REDUCE function. |
| lambda | Parameter of the REDUCE function. |
Examples
Running product (multiply all values)
Formula
=REDUCE(1, A1:A5, LAMBDA(acc, val, acc*val))
Returns the product of all values in A1:A5. Starts with 1, multiplies by each value in sequence. If values are 2,3,4,5,6 the result is 720.
Concatenate with delimiter
Formula
=REDUCE("", A1:A5, LAMBDA(acc, val, IF(acc="", val, acc&", "&val)))
'Apple, Banana, Cherry, Date, Fig'. Builds a comma-separated string from the list without a leading comma.
Count values meeting a condition
Formula
=REDUCE(0, B1:B100, LAMBDA(count, x, count + IF(x>50, 1, 0)))
Counts how many values in B1:B100 exceed 50. Equivalent to COUNTIF but demonstrates REDUCE's flexibility.
Common Errors
#VALUE!
The LAMBDA doesn't accept exactly 2 parameters (accumulator and current value).
#CALC!
The LAMBDA body produces an error during iteration, halting the reduction.
Tips
Initial value matters
Use 0 for sums/counts, 1 for products, "" for string concatenation. The initial value is what the accumulator starts at before the first element.
LAMBDA receives (accumulator, current_value)
The first parameter is the running result from all previous iterations. The second is the current array element being processed.
Use when SUM/PRODUCT aren't enough
REDUCE shines for custom aggregations that built-in functions can't handle, like conditional string building, running max/min with logic, or multi-step accumulations.
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