sort array with two columns

[Booth Martin <booth@xxxxxxxxxxxx>]

This has to be easier than I am making it.

Lets say I have field FirstName and field LastName with, say, 15 rows 
out of an array size of 100.

I want users to be able to sort by:

 * FirstName (A)
 * FirstName (D)
 * LastName (A)
 * LastName (D)

I can do that with sorta %subArr(field: 1: 15) and sorta(d) 
%subArr(field: 1: 15).

However getting the complete first & last name to sort together is 
convoluted, so my guess is I am missing something simple.