I have the following data structure
Date Agric Food
01/01/1990 1.3 0.9
01/02/1990 1.2 0.9
I would like to covert it into the format
Date Sector Beta
01/01/1990 Agric 1.3
01/02/1990 Agric 1.2
01/01/1990 Food 0.9
01/02/1990 Food 0.9
while I am sure I can do this in a complicated way, is there a way of doing this in a few line of code?