In advance: Sorry for all the Norwegian references, but I hope I've explained my problem good enough for them to still make sense...

So, in 2005 Norway got a new criminal law. The old one was somewhat unstructured (only three chapters), while the statutory provisions in the 2005 version have been structured into 31 chapters, depending on the area of the offense (can be seen here: https://lovdata.no/dokument/NL/lov/2005-05-20-28). I call these "areas of law". For example, in the 2005 version laws regarding sexual offenses are in chapter 26. Logically, then the statutory provisions that belong to this chapter are categorized as belonging to the area of law called "s

Some of the old laws have been structured into the new chapters, some new have been added, and some have been repealed. I have what is called a "law mirror" – a list where you can find where the old provision are in the new law, if it hasn't been repealed. The new law came into force for offenses committed from the 1st of October in 2015.

An example of a law mirror: https://no.wikipedia.org/wiki/Straffeloven_(lovspeil). I've pivoted the list longer, such that it looks like this:

Law Mirror: "Seksuallovbrud" means sexual offense, "kap_2005" says which chapter in the 2005 law that the statutory provision (norwegian: "paragraf") falls under, and "straffelov" specifies whether the provison comes from the 2005 or 1902 version of the law.

The data I have consist of two separate data frames. Df1 is the law mirror. Df2 consists of cases in the Norwegian court of appeals from between 1993 and 2019, where the criminal law was the basis of the verdict. I've made a dummy (strl1902) in Df2 for whether the verdict in the case came before or after the new law came into force. Equal to 1 if it's the old one. I've also extracted the number of the statutory provision.

On the basis of this I want to categorize the cases using statutory provisions from the old criminal law into the areas of law from the new law.

This is where I need help:

Do any of you have any idea of how I can distinguish between the provisions from the old and the new law, such that I also can make dummies for the provisions from the 1902 law, such that they are separated into the areas of the law of the 2005 law?

Hope this makes sense.