Rows with different schema

[fg5]

I have some timetable data for classes that is formatted in such a way that rows have different schema.

The first few rows define the column header for each different schema, one for CLASS, one for TIME and some others (removed for simplicity).

Any given TIME row will be related to the CLASS above it, and one class can have multiple times.

Nothing else relates a TIME to a CLASS other than its relative position.

Example:

CLASS	NAME	TERM	YEAR
TIME	START	END
CLASS	Mathematics 1	T1	2023
CLASS	Mathematics 2	T1	2023
TIME	14:00	15:00
TIME	16:00	17:00
CLASS	English	T2	2023

Here you can see only Mathematics 2 has classes, one from 14:00 to 15:00, and 16:00 to 17:00.

I want to turn each TIME row into a column in its corresponding CLASS as a list of records:

NAME	TERM	YEAR	TIME
Mathematics 1	T1	2023
Mathematics 2	T1	2023	<List of TIME Records>
English	T2	2023

Doing it in PowerShell or OfficeScript is trivial, but I need it in M.

I've tried accumulators, recursion, and a bunch of other stuff, but always hit a wall.

I have limited experience with functional programming and I feel like I'm fighting M, so my imperative programming brain must be getting in the way.

Any ideas?

[wdx223_Daniel]

let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcvZxDA5WUNJR8nP0dQVSIa5BvkAq0tUxSClWJ1opxBMsHBziGBQCpF39XICkAlgKrBXI800syUjNTSzJTC5WMAQZASKMDIyMcaoywlAFtcbQxMrAAESbQmgFFEkzqKQ5siTMfNe89JzM4gyQyUZwk2MB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Column1 = _t, Column2 = _t, Column3 = _t, Column4 = _t]),
Custom1 = Table.Combine(Table.Group(Table.Skip(Source,2),"Column1",{"n",each if Table.RowCount(_)=1 then _ else Table.FromColumns(List.Zip({Record.ToList(_{0})})&List.Range(Table.ToColumns(Table.Skip(_)),1,2))},0,(x,y)=>Byte.From(y="CLASS"))[n])
in
Custom1