Excel formula to dynamically reference a range using values from a horizontally and vertically spilled ranges

[cadams1979]

I have 2 dynamic arrays; one for the first column of data (vertical) and a second for a header row (horizontal) which together make up a grid view.

I need a formula that will spill dynamically when there are changes to either the horizontal or vertical ranges. I want to use the combination of the values from each array (horizontal & vertical) to FILTER another range and show the cells found with a TEXTJOIN for a comma delimited string.

I can perform a COUNTIF relatively easily with verticalarray#&horizontalarray# and that works nicely but every time I attempt with FILTER I get an error

Anyone out there have any smart ideas in how they can help?

Here's quick dump of the data examples

 

[cadams1979]

I believe I've solved it...

	C1	C2	C3
R1				R1C1
R2				R2C1
R3				R3C1
				R1C2
				R2C2
				R3C3
				R1C1
				R2C1
				R3C1
				R1C2

=SCAN("",$A$2#&$B$1#,LAMBDA(a,b,IFERROR(TEXTJOIN(",",TRUE,FILTER($E$2:$E$10,b=$E$2:$E$10)),"")))

R1C1,R1C1	R1C2
R2C1,R2C1	R2C2
R3C1,R3C1		R3C3