irule extract subset query params and alphabetize

f5 BIG-IP 11.4.0 LTM VE

In an iRule , what is most performant way to extract a subset of HTTP:query params and alphabetize.

HTTP:query = a=1&c=3&b=2&n=1&m=3&p=2

transformed = a=1&b=2&c=3

HTTP:query can have an arbitrary number of query params