Re: Ascend and data structure lookups.

On Nov 25, 2015, at 10:40 PM, Booth Martin <booth@xxxxxxxxxxxx> wrote:

This was the question that was not clear to me. It looked like, from various sources, that %lookup always does a binary search, even if the ascend/descend keyword isn't used; and thus could provide unexpected results on an unordered array. Yet, from other sources, it looked like %lookup would look for the keyword and if it was not present, flip over to a row-by-row look-up.

On 11/25/2015 4:13 PM, Jon Paris wrote:

But will ONLY perform a binary search if the Ascend/Descend keyword is present.

The OPs problem was that using an externally described DS (which keeps SQL happy) left no opportunity to specify the keyword since it is not “legal” at the DS level.

The SQL will have ordered the result set, so no sort needed and the binary search will work fine if only the keyword can be specified.

On Nov 25, 2015, at 4:54 PM, Booth Martin <booth@xxxxxxxxxxxx> wrote:

%lookup is a binary search.

"...The %LOOKUPxx built-in functions use a binary search for sequenced arrays (arrays that have the ASCEND or DESCEND keyword specified). ..."

http://www-01.ibm.com/support/knowledgecenter/SSPSQF_9.0.0/com.ibm.etools.iseries.langref.doc/evfrilsh855.htm

On 11/25/2015 3:16 PM, Alan Campin wrote:

Issue is not sort of data. Data is loaded by an SQL in key order. What I am
wanting to do is do a binary search on the data. I know it is in the right
order. A solution that I know works is to use bsearch. I was just trying to
figure out if IBM had a way to do the binary search on a lookup over a data
structure. As far as I know they don't. Just trying to see if someone has a
way to make it work.

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Jon Paris

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www.SystemiDeveloper.com

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