New transform utility functions

[rompetroll]

It is a common transform requirement to create a new URI based on an exiting URI, just with a different namespace.

For example, in a transform loop we filter a population dataset and produce a new dataset only containing adults. When we process an entity with entity.ID="ns24:17", where ns24 is a prefix for http://people/. And we want the outgoing entity after filtration to have entity.ID="ns25:17", where ns25 stands for http://adults/.

Currently, this has to be solved using manual string splitting and concatination. E.g.

const adultsPrefix = AssertNamespacePrefix("http://adults/");
SetId(newEntity, adultsPrefix + ":" + GetId(e).split(":").pop())

I am not sure what the utility function(s) should look like exactly. Maybe something like this:

const newId = WithNamespacePrefix(GetId(e), adultsPrefix);
SetId(newEntity, newId)

It would not be much conciser, but add robustness for this common use case.

A utility function to extract the namespace/namespace prefix from URIs without manual string splitting would also be welcome.