Unpivot by groups

[BobKoenen]

Hi All, 

I have a table which looks like this but in reality has 20 Atr columns

Customer	Atr A1	Atr B1	Atr C1	Atr A2	Atr B2	Atr C2	Atr A3	Atr B3	Atr C3
A	Purple	Iron	kids	Yellow	Plastic	Teens	Pink	Paper	Senior
B	Green	Plastic	Adult	Black	Plastic	Adult	White	Wood	Kids

And I want it to look like this 

Customer	Atr A	Atr B	Atr C
A	Purple	Iron	Kids
A	Yellow	Plastic	Teens
A	Pink	Paper	Senior
B	Green	Plastic	Adult
B	Black	Plastic	Adult
B	White	Wood	Kids

Have you got any Idea how to fix this?

[CNENFRNL · Accepted solution]

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("bY5BCoQwDEXvkrWX0M0gbgQFGUoXxQYmNDQSK17fZCnM6v3wfuCHAD10MF96MFoYVaqhUD4NX2SW2z2ns9FuaUWsrmaqxZEOVOOClUQhdgEGOz9qtddfny9uxoHTXv6a7UfNJ2wi2TD5hBgf", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Customer = _t, #"Atr A1" = _t, #"Atr B1" = _t, #"Atr C1" = _t, #"Atr A2" = _t, #"Atr B2" = _t, #"Atr C2" = _t, #"Atr A3" = _t, #"Atr B3" = _t, #"Atr C3" = _t]),
    Transformed = let cols = Table.ToColumns(Source), hdr = cols{0} in Table.Combine(List.Transform(List.Split(List.Skip(cols),3), each Table.FromColumns({hdr} & _)))
in
    Transformed