Re: Keyed Array Data Structures

[Mark Waterbury <mark.s.waterbury@xxxxxxxxxxxxx>]

 Vinay,
A binary search is exactly what %lookup does.  For that algorithm to work correctly, you must ensure that the table or array is sorted properly.
See:    https://www.rpgpgm.com/2015/09/when-lookup-ne-lookup.html


Excerpt from the above article below:
Referring to IBM's KnowledgeCenter I found a link at the bottom of the %LOKUPxx page that took me to a page called: Sequenced arrays that are not in the correct sequence ... an interesting passage on this page states:

... the %LOOKUPxx built-in functions and the LOOKUP operation code may find different values. The %LOOKUPxx built-in functions may not find a data value even if it is present in the array.

Since a binary search is used by the %LOOKUPxx built-in functions for a sequenced array, and the correct function of a binary search depends on the data being in order, the search may only look at a few elements of the array. When the array is out of order, the result of a binary search is unpredictable.


See:   
   - %LOOKUPxx BIF
   - LOOKUP Operation code
   - Sequenced arrays that are not in the correct sequence


See also:   http://www.itjungle.com/fhg/fhg020409.html


Hope that helps,
Mark S. Waterbury

    On Friday, December 2, 2022 at 09:25:54 AM EST, Vinay Gavankar <vinaygav@xxxxxxxxx> wrote:  
 
 Hi,

Is there a way to define a "sequenced" keyed array data structure, so that
the  system uses Binary Search when doing a %lookupxx on it using the key?

TIA
Vinay