How to use group by in xslt

Question

I have a xml that has so many elements and most of that contain attributes.. for some of the attributes values are same so I need to group them and generate diff xml. I/p Ex

Answer 1

In XSLT 1.0 you would use Muenchian grouping.

Define a key "format", from which we can easily select all elements given a format name. Than apply Muenchian grouping to find the unique formats in the input.

Then it gets simple. The "*" template will be applied once per format, and uses the key() to fetch all entries for that format.