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1Repair Windows errors before they cause bigger problems2Fix the driver behind crashes, sound loss and screen glitches3Clear out junk files and repair common Windows errorsUse SCAN with LAMBDA when you want Excel to process an array one item at a time and return every intermediate result—not just the final total. The key is to give the LAMBDA a starting state, the accumulated result so far, and the current item, then define how those two values produce the next state.
How SCAN and LAMBDA work together
Microsoft describes SCAN as applying a LAMBDA to each value in an array and returning the intermediate values. Think of it as a repeating rule:
New accumulator = calculation using the previous accumulator and the current item.
SCAN passes the accumulator forward from one item to the next. Its result is an array containing each updated accumulator, so it is useful when you need to see a running progression such as cumulative totals, products, or text.
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Understand the arguments
The general syntax is =SCAN([initial_value], array, LAMBDA(accumulator, value, body)). In a formula, the LAMBDA’s final expression is the calculation that returns the next accumulator.
initial_value: the starting state. Use a value that fits the calculation, commonly0for addition,1for multiplication, or""for text concatenation.array: the range or array whose items SCAN processes.accumulator: the result carried forward from the preceding step. It is the first parameter in the inner LAMBDA.value: the current item from the input array. It is the second parameter in the inner LAMBDA.body: the expression that combines the accumulator and current value to return the next accumulator.
Parameter names are labels, not reserved keywords. For example, LAMBDA(a,v,a+v) means “add the current value v to the prior accumulated result a.” Choose clear names if they make a longer formula easier to follow. Microsoft’s LAMBDA documentation says parameter names follow Excel naming rules, except they must not contain a period; a LAMBDA can have up to 253 parameters, and its calculation must be its last argument and return a result.
Build common running calculations
Running total
For numbers in A1:A5, enter:
=SCAN(0,A1:A5,LAMBDA(a,v,a+v))SCAN starts at zero, adds each current value to the running total, and returns the updated total at each position. For instance, if the input is 2, 4, and 3, the returned progression is 2, 6, and 9.
Running product
To multiply each item by the accumulated product, start with one:
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=SCAN(1,A1:A4,LAMBDA(a,v,a*v))Microsoft’s documented product example is =SCAN(1, A1:C2, LAMBDA(a,b,a*b)); it presents the formula as creating a list of factorials. The actual output depends on the values in the referenced cells.
Cumulative text
To append each item to the text collected so far, use the empty string as the initial value and Excel’s concatenation operator, &:
=SCAN("",A1:C2,LAMBDA(a,b,a&b))Microsoft documents this pattern. Each output includes the text accumulated through that position.
Other stateful patterns
Any calculation that depends on both the previous state and the current item can fit the same structure. These illustrative patterns use a running maximum and a count of values above a threshold:
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=SCAN(0,A1:A5,LAMBDA(a,v,MAX(a,v)))Here, MAX(a,v) keeps whichever is larger: the previous maximum or the current value.
=SCAN(0,A1:A5,LAMBDA(a,v,a+(v>10)))Here, v>10 evaluates to TRUE or FALSE, which Excel treats as 1 or 0 in this arithmetic expression; adding it to a increments the running count only when the current value is greater than 10.
Choose SCAN or another helper
Microsoft’s logical functions reference describes several LAMBDA helpers. Pick one based on the shape of the result you need.
| Function | What it returns | Use it when |
|---|---|---|
SCAN |
Every intermediate accumulated result | You need 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 from applying a LAMBDA by row or column | The calculation should operate at row or column granularity. |
Fix common formula errors
#VALUE! — Incorrect Parameters
Microsoft says SCAN returns #VALUE! with the label “Incorrect Parameters” when its LAMBDA is invalid or has the wrong parameter count. Check that the outer call supplies the initial value, array, and LAMBDA in that order; that the inner LAMBDA accepts both the accumulator and current value; that the body returns a value; and that parentheses and argument separators match.
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Excel formula separators can vary by locale. If your Excel expects semicolons, replace the commas in examples with semicolons.
#CALC! — LAMBDA entered without being called
A bare LAMBDA definition entered in a cell without arguments to call it returns #CALC!, according to Microsoft’s LAMBDA error notes. Test a LAMBDA by immediately calling it in a cell, as in Microsoft’s example:
=LAMBDA(number, number + 1)(1)This returns 2. Testing a calculation this way can help isolate a problem before adding it to SCAN.
#NUM! — Recursive-call limit
Microsoft also notes that a LAMBDA can return #NUM! after too many circular recursive calls. That is a general LAMBDA issue, distinct from SCAN’s documented incorrect-parameter error.
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Check function availability and save a reusable LAMBDA
Microsoft lists SCAN and LAMBDA for Excel for Microsoft 365, Excel for Microsoft 365 for Mac, Excel 2024, and Excel 2024 for Mac on their function pages. The alphabetical function catalog marks both as introduced in 2024. If you use an older perpetual edition, verify that the functions are available in your Excel before building a workbook around them; Microsoft’s cited pages do not specify a more precise rollout date or build number.
After a LAMBDA works when called directly, you can save it as a reusable custom function with a descriptive name. Microsoft says to use Name Manager in Excel for Windows or Define Name on Mac. Workbook scope is the default; sheet scope is also available, except in Excel for the web.
For Microsoft’s documented syntax, examples, and error notes, see the SCAN function and LAMBDA function pages.
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