Deconstructing a table - How to take a table back to the begining

Hi,
I have a table with column A populated with identifiers and a dynamic number
of cols to the right storing the weights of different products. For example
say columns B - M. I would like to un-build the table such that the result
is a long list of three columns.
Col A = Value of ID at row(i)
Col B = Value of Header (product name)
Col C = Value of weight at row(i)

Col A | Col B | Col C
A2 B1 B2
A3 B1 B3
A4 B1 B4
A2 C1 C2
A3 C1 C3
A4 C1 C4

etc...

I was thinking of doing this with a 2D array. Is that the right place to
start? Is there a better approach? If 2D array is the way to go, hmm, where
should I start?

Thanks for your help!