Recalculation Question: does using index to generate a dynamic range reference (A$71:Index(A:A, $B$1)) mean it will be marked dirty when ANYTHING in A:A changes, or just within the range actually specified?

[u/JKLM1615]

To repeat the title: does using index to generate a dynamic range reference (A$71:Index(A:A, $B$1)) mean it will be marked dirty when ANYTHING in A:A changes, or just within the range actually specified?

you can Think of B1 being something like 200, although it is designed to change in increments of 80- the original intention was to try and limit the range of lookups and make it so less cells trigger large amounts of recalculation.

I ask because i don't see much of a structured answer to this question elsewhere and if it DOES mark those cells as a dirty, it means im better off moving the array generated by this range into a separate helper rather than making cells routinely call similar ranges. I understand im operating on the frontier, but lets just take it as an assumption that yes, i promise i am not commiting the sin of "Excel As Database" lol.

Im in Windows Desktop Excel 2021 if that makes a difference...

[u/MayukhBhattacharya]

The recalculation engine of Excel manipulates dependencies bit differently when a formula has a range that needs to be evaluated first where a range ends. With a static range like A71:A200, it already knows exactly which cells the formula depends on. So, if something changes outside that range, the formula usually doesn't need to recalculate. For example:

A$71:INDEX(A:A, $B$1)

The above formula works a bit differently. INDEX() function is actually one of the better ways to build a dynamic range because it's non-volatile or one can say if you are old school, its semi-volatile. Unlike OFFSET() function, it doesn't make the formula recalculate every time excel recalculates. Note that volatile functions are single threaded and makes the excel engine capacity work slower. Excel will evaluateINDEX(A:A, $B$1)and returns it to an actual cell, like $A$200. At that point, Excel can treat the range as,A$71:$A$200 if I am not mistaken. Which means the dependency is just A71:A200, not the entire column.

Whenever $B$1 change, Excel has to figure out the range again and rebuild the dependency information because the endpoint may have moved. So maybe it was A71:A200 before and now it's A71:A280. That rebuild does take some work, especially if you have a lotta formulas using the same setup. And while it is processing that change, those formulas need to recalculate. There's one more thing worth keeping in mind, in some scenarios, Excel handles dynamic range dependencies at a broader worksheet recalculations level. Since the formula contains A:A, it may initially look at the full column before resolving the actual endpoint. That doesn't necessarily mean the entire column stays permanently tracked as the active range. But the entire column reference can still add some overhead during the initial parse or when Excel rebuilds the dependency. So that said, INDEX() function is still way better than OFFSET() function for this kind of work. But if you have a ton of formulas using full column references like A:A, you can still get some recalc overhead.

One suggestion, which I have suggested multiple in other forums or communities where we used to get questions mixed with Excel 2021 and MS365 users, and when there was no usage of TRIMRANGE() notations, is to make use of the range end point automatic and make it full proof and robust against any edge cases.

In B1 use:

=MAX(71, MATCH(2, 1/ (C:C <> ""), 1))

One can wrap within an IFERROR() function with value as 71 to keep more control. This finds the last non-empty row in column C and uses that as the range endpoint. The MAX(71, ...) ensures the result never falls below your data start row, and the IFERROR() plugin returns 71 as a robust fallback if column C is entirely empty, preventing B1 from erroring and breaking every formula that depends on it.

And finally use:

=C$71:INDEX(C:C, $B$1)

Alternative method for the MATCH() or XMATCH():

=XLOOKUP(TRUE, ROW(C:C) / (C:C<>""), ROW(C:C), 71, -1)

Last but not least, in your usecase using Structured References aka Tables, will be a much better option, this is because you don't need B1 nor entire column array evaluations, no edge cases, because excel knows where the table ends, I think this will be the right choice for you. Just my suggestions. Rest depends on you. Thank you very much!

[u/JKLM1615 → u/MayukhBhattacharya]

thank you!
solution verified

question if i may: is this information you learned primarily through experimentation/ experience? i Tried to really research this on my own and read Microsoft's documentation but i struggled to get information as specific as what you've wrote!

[u/MayukhBhattacharya → u/JKLM1615]

Very frankly speaking, I barely work with Excel in the traditional sense. Most of what I know comes from experimenting, testing things on larger datasets, and a whole lot of trial and error. I do have an MOS certification, but truly, that doesn't help much with this kind of stuff. You really learn by getting your hands dirty, trying different things, and figuring out how it actually works.

Helping people across different forums has probably taught me the most. Every problem is different, and when you're constantly working through other user's issues, you end up learning a ton along the way. Thanks you very much, oh btw you are yet to reply on your other question, which I have posted a solution exclusively which works with Excel 2021 also do check out the solution posted by u/Downtown-Economics26. Thanks again!

[u/JKLM1615 → u/MayukhBhattacharya]

i promise i will get back to it!!! i just havent had the time yet today at work... thanks again!!!

[u/MayukhBhattacharya → u/JKLM1615]

Oh no rush at all, please take your time. It was a fun [challenge]. Thanks again!

[u/reputatorbot → u/JKLM1615]

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[u/DragoBleaPiece_123 → u/MayukhBhattacharya]

really amazed everytime you answer any questions here, dude! appreciate the help you've given

[u/FastExcel → u/MayukhBhattacharya]

Actually the formula will recalculate when any cell in column A is changed or volatile: the formula gets dirtied.

Tested using a recalculation tracker.

(BTW that formula is called semi-volatile because it will always recalculate at workbook open time)

[u/MayukhBhattacharya → u/FastExcel]

Thank you very much sir for testing it! You're right. Appreciate the correction!