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How SCAN and LAMBDA work together
Microsoft describes SCAN as scanning an array by applying a LAMBDA to each value and returning an array of intermediate results. Its syntax is:
=SCAN([initial_value], array, LAMBDA(accumulator, value, body))
Think of the LAMBDA as an update rule: new accumulator = a calculation using the old accumulator and the current item. SCAN starts with the initial value, applies that rule to the first item, carries the result forward, and repeats for each item. The returned array contains the result at each step.
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initial_valuesets the accumulator’s starting state. Use0for a running sum,1for a running product, or""for text concatenation. Microsoft specifically recommends an empty string when working with text.arrayis the range or array whose values Excel processes.accumulatoris the result carried over from the previous step.valueis the current item in the array.bodyis the expression that calculates the next accumulator. In the examples below,LAMBDA(a,v,a+v)means “add the current value,v, to the prior accumulated result,a.”
The parameter names are labels you choose; they do not have to be literally accumulator and value. Follow Excel’s naming rules, including its restriction against periods in parameter names. The LAMBDA calculation expression must be its final argument and return a result. See Microsoft’s SCAN function documentation and LAMBDA function documentation.
Build a running calculation
Running total
If the numbers are in A1:A5, enter:
=SCAN(0,A1:A5,LAMBDA(a,v,a+v))
Excel starts at zero, adds each current cell to the total so far, and returns the successive totals as a spilled array. For example, if the cells contain 2, 4, and 3, the corresponding results are 2, 6, and 9.
Running product
For a cumulative product over a vertical range such as A1:A4, use:
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=SCAN(1,A1:A4,LAMBDA(a,v,a*v))
The starting value is one, and each step multiplies the previous product by the current value. Microsoft’s documented product example uses a two-dimensional range:
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=SCAN(1, A1:C2, LAMBDA(a,b,a*b))
Microsoft describes this as creating a list of factorials; the actual results depend on the values in the supplied range.
Cumulative text
To append each value in a range to the text accumulated so far, use an empty string as the initial value:
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=SCAN("",A1:C2,LAMBDA(a,b,a&b))
The & operator joins the prior text and current value, so the output contains progressively longer concatenations. This is Microsoft’s documented text pattern.
Other stateful patterns
The same structure can update a running state in other ways. These are illustrative patterns derived from the accumulator rule:
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=SCAN(A1,A1:A5,LAMBDA(a,v,MAX(a,v)))carries forward the larger of the prior maximum and current value. Starting withA1includes the first item as the initial maximum. - Conditional running count:
=SCAN(0,A1:A5,LAMBDA(a,v,a+(v>10)))adds one when the current value is greater than 10 and otherwise keeps the count unchanged. Replace10with the threshold you need.
Choose SCAN when you need every step
SCAN is one of several Excel functions that use LAMBDA expressions. Choose among them based on the shape of the result you need:
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| Function | What it returns | Use it when |
|---|---|---|
SCAN |
Each intermediate accumulated result | You need to see the running progression. |
REDUCE |
The final accumulated result | You need only the final aggregate or state. |
MAP |
An array of transformed values | Each item should be transformed independently. |
BYROW / BYCOL |
Results of applying a LAMBDA by row or column | The calculation should operate at row or column granularity. |
Microsoft summarizes these functions in its logical functions reference.
Check that your Excel version includes SCAN
Microsoft lists SCAN and LAMBDA for Excel for Microsoft 365, Excel for Microsoft 365 for Mac, Excel 2024, and Excel 2024 for Mac. Its alphabetical function catalog marks both as introduced in 2024; that marker identifies the introduction version, not a more specific rollout date or build. If you use an older perpetual edition, check whether the functions are available in your copy before building a workbook around them. See Microsoft’s alphabetical function catalog and function catalog by category.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot SCAN and LAMBDA formulas
#VALUE! with “Incorrect Parameters”
Microsoft says SCAN returns #VALUE! with “Incorrect Parameters” when its LAMBDA is invalid or has the wrong parameter count. Check that the arguments to SCAN are in this order: initial value, array, LAMBDA. The inner LAMBDA needs to accept the accumulator and current value, and its calculation must produce the next result. Also check that parentheses and your locale’s argument separators match.
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#CALC! from a bare LAMBDA
A LAMBDA entered by itself in a cell without being called returns #CALC!. Test a LAMBDA by calling it directly in a cell first:
=LAMBDA(number,number+1)(1)
This immediate call returns 2. Once a more complicated LAMBDA works, you can make it reusable through Name Manager in Excel for Windows or Define Name on Mac. Workbook scope is the default; sheet scope is also available, while Excel for the web does not offer sheet scope. Microsoft’s LAMBDA documentation also notes that a LAMBDA can accept up to 253 parameters and that too many circular recursive calls can produce #NUM!; those are general LAMBDA behaviors, not SCAN’s incorrect-parameter message.
Formula separators and spilled results
If your Excel locale uses semicolons between arguments, replace the commas in the examples with the separators your Excel expects. SCAN returns an array of intermediate values, so the output needs room to spill into adjacent cells; clear any cells blocking the intended result area if Excel cannot display the array.
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