Excel ; Accumulate by month using LAMBDA

Hi,
is there a way to write a lambda, probably using scan, to give a recurring accuulation by month for the Date format dd / mm/ yyyy

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the abvoe is just working on a list of numbers and resets each time a one occurs, I could use this method, with a DAY function to get if = 1
but not all the months are going to have 01 as there first date,

Just using excel would be ;

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so I need a way to trigger a reset at the min date of each month?

Richard

examples attached.

Well, I haven't been able to get the result I want? but the equivalent of

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but using a LAMBDA, either scan or MAP ?

So it resets for each month.

How about

Formula:

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I'll have to spend some time working through that I'll let you know how I get on.

The Month Tab, RTC column.

Another option is

Formula:

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Another way,

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Re the let sequence matrix * torow matrix, it certainly works, but having spent some time dissecting it , still not sure quite how it does.

Thank you to all who responded I think I have enough to make make my head hurt for a few days

Glad to help & thanks for the feedback.

You are welcome.
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