LINEST with start/end conditions to select data.

[Josephfdebartolo]

I'm looking to predict data in pumping applications. given this. I will have unknow lengths of tables that will constantly have data added and removed.
I can't find a way to structure the selected data the way I would like it to be.

All data is expected to be quadradic, so my basic LINEST is =LINEST(C23:C33,B23:B33^{1,2},TRUE,FALSE)

I would like the formula to be along the lines of LINEST, Y DATA, from when first value in C23 to C54 is greater then 20% of starting flow, and to stop on last data point. X to be used if y data is used, skipped if y is skipped
=LINEST('for y values' IF(C23 > .2*A3,C23,SKIP):LAST CELL <> BLANK, 'for x values' start when y starts:end when y ends^{1,2},TRUE,FALSE)

there is a max of 50 data points, starting at row 23, and I have been manually selecting the data to make the equation work. but there is ALOT of (40 some) functions being manually edit. so looking to stream line it to auto select the data given the starting and end conditions.

View attachment 76431

 

[Anthony47]

This looks a bit overcomplicated, but might (might) work:

=LET(aArr,C23:C33,bArr,B23:B33,Thresh,A3*0.2,fromR,SMALL(IF(aArr>Thresh,ROW(aArr),99999),1),gRows,SEQUENCE( ROWS(aArr)-fromR+SMALL(ROW(aArr),1),,1+fromR-SMALL(ROW(aArr),1)),LINEST(INDEX(aArr,gRows),INDEX(bArr,gRows)^{1,2},TRUE,FALSE))

Try...

 

[Josephfdebartolo]

This will take me a minute to understand what's going on. the starting condition does work so that is a massive step forward, but if the data length is shortened or increased, the formula doesn't find the new end. Thanks for the info and I'm going to see if I can make it completely work with some tweaking.

 

[Anthony47]

A simple way could be creating two dynamic ranges, NameC that refers to values in column C and NameB that refers to values in column B; the in the formula you modify aArr,C23:C33,bArr,B23:B33, to

aArr,NameC,bArr,NameB,