Google sheet array formula with Filter & Join - google-sheets

Question

I need to build a table based on the following data:
Ref
Product
R1
ProdA
R2
ProdC
R1
ProdB
R3
ProdA
R4
ProdC
And here the result I need:
My Product
All Ref
ProdA
R1#R3
ProdC
R2#R4
The particularity is that the 'My Product' column is computed elsewhere. So I need an arrayformula based on 'My Product' column to look in the first table to build the 'All Ref' column. You follow me?
I know that Arrayformula is not compatible with filter and join ... I expect a solution like this one Google sheet array formula + Join + Filter but not sure to understand all steps and if really adapted to my case study.
Hope you can help.

Answer 1

You could try something like this:
CREDIT: player0 for the method shared to similar questions
=ARRAYFORMULA(substitute(REGEXREPLACE(TRIM(SPLIT(TRANSPOSE(
QUERY(QUERY({B2:B&"😊", A2:A&"#"},
"select max(Col2)
where Col1 !=''
group by Col2
pivot Col1"),,999^99)), "😊")), "#$", )," ",""))
Step by step:

Answer 2

Instead of the workaround hacks I implemented a simple joinMatching(matches, values, texts, [sep]) function in Google Apps Script.
In your case it would be just =joinMatching(MyProductColumn, ProductColumn, RefColumn, "#").
Source:
// Google Apps Script to join texts in a range where values in second range equal to the provided match value
// Solves the need for `arrayformula(join(',', filter()))`, which does not work in Google Sheets
// Instead you can pass a range of match values and get a range of joined texts back
const identity = data => data
const onRange = (data, fn, args, combine = identity) =>
Array.isArray(data)
? combine(data.map(value => onRange(value, fn, args)))
: fn(data, ...(args || []))
const _joinMatching = (match, values, texts, sep = '\n') => {
const columns = texts[0]?.length
if (!columns) return ''
const row = i => Math.floor(i / columns)
const col = i => i % columns
const value = i => values[row(i)][col(i)]
return (
// JSON.stringify(match) +
texts
.flat()
// .map((t, i) => `[${row(i)}:${col(i)}] ${t} (${JSON.stringify(value(i))})`)
.filter((_, i) => value(i) === match)
.join(sep)
)
}
const joinMatching = (matches, values, texts, sep) =>
onRange(matches, _joinMatching, [values, texts, sep])```