Stack multiple columns in a single column based on another column - google-sheets

Question

In sheet1, I have something like this (A to D are headers - sample sheet here):
A
B
C
D
X
X1
X2
Y
Y1
Y2
Y3
Z
Z1
And in sheet2, I want something like this:
A
B
X
X1
X2
Y
Y1
Y1
Y1
Z
Z1
*Values in column A exists only on the first instance (it's not merged with the cells below it)
Sheet1 data comes from google form submissions, but we want to structure them as to the table sample in sheet2, where sheet1 columns B to D are stacked in sheet2 column B.
For now, we're using the following to merge columns B to D in a single cell aligned with the values in column A:
=ArrayFormula(Sheet1!A:A&CHAR(10)&Sheet1!B:B&CHAR(10)&Sheet1!C:C&CHAR(10)&Sheet1!C:C&CHAR(10)Sheet1!D:D)
However, this presents a lot of problems since line breaks would still be there even when there's no supposed second line, and that we have to manually update status of these items (since they're used for monitoring).
If we can have it line by line as what is expected, we'd be able to automate some of the tasks. We tried playing with QUERY, but to no avail (although I think it's possible via that function... not sure).
Hoping to get ideas from the community. Thanks!

Answer 1

I've added a new sheet ("Erik Help") with the following formula in A1:
=ArrayFormula({"Header 1", "Header 2";QUERY(SPLIT(FLATTEN({FILTER(INDIRECT("Sheet1!A2:A"),INDIRECT("Sheet1!A2:A")<>"")&"|"&FILTER(INDIRECT("Sheet1!B2:B"),INDIRECT("Sheet1!A2:A")<>""),IF(FILTER(ROW(INDIRECT("Sheet1!A2:A")),INDIRECT("Sheet1!A2:A")<>""),"")&"|"&FILTER(INDIRECT("Sheet1!C2:D"),INDIRECT("Sheet1!A2:A")<>"")}),"|",1,0),"Select * Where Col2 Is Not Null")})
This formula creates the two headers first.
You'll notice the heavy use of INDIRECT to reference ranges. This is because you'll have form data coming into that sheet; and if the formula doesn't have a way to "lock" ranges, those ranges will shift down one every time a new row is added onto the form-intake sheet. In most other applications, you can "lock" those ranges by using full-column references (e.g., A:A instead of A2:A). But given the specifics of what you're trying to do here, INDIRECT was the least complex approach. Keep in mind that, because INDIRECT is used, the references will not automatically change if you rename Sheet1 to something else (like "Form Responses 1"). You will need to change each reference manually. Or use FIND/REPLACE, select "Specific Range" set to the formula cell, and check the "Also search within formulas" box.
The idea here is that every value from A2:A is concatenated to every value in the same row of B2:D, with a pipe symbol between (as a SPLIT marker for later). Since you only want to see the Col-A values beside Col-B values, Col-A&"|"&Col-B are first processed alone; then a blank is appended instead of Col-A for everything else.
FILTER is used to only process rows for which there is data in Col-A.
SPLIT splits the combinations made (as described above) at the pipe symbol, forming two columns.
QUERY keeps only those results of the SPLIT that have something in the second column.