Data structure array with lookup on subfield?

Hello,

I want to create a dynamically allocated array to store popular
searches with each element storing a pointer, return code and field
name like below:

Struct DS Dim(32767)
Based(pStruct)
Ptr *
Retcod 10i 0
field 10a
* define array over subfield of structure
fieldarr 10a Dim(32767) Overlay(field)

Now I want to allocate elements as needed and populate the structure.
The problem I have is that I want to be able to do a lookup on the
field part of the structure (which is basically the key), something
like

pos = %lookup(Infield: fieldarr : 1: lastelemfilled);

Which would tell me if an element with the infield value already
exists and if so I would use the ptr and rtncod fields from that
element otherwise I would allocate memory and add another element to
Struct.

Unfortunately I have not been able to figure out how to do this, the
multiple entries in struct with the DIM keyword work fine but I can't
figure out how to define an array over the field subfield.

Any help with this would be appreciated.

Paul