RE: Problem using tlookup bif

Well, Bob is certainly good but there ain't none of us always right. :)
(How's that for good grammar?)

Here's something from Barbara on this topic:

%lookup performs faster than LOOKUP if you have a sequenced array, because
it can do a binary search. But it looks like your array data isn't
sequenced, so %lookup will have similar perforamance to LOOKUP.

http://forums.systeminetwork.com/isnetforums/showthread.php?t=51199

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
LARGER KANGAROOS LEAP FARTHER, RESEARCHERS FIND
-- headline from the Los Angeles Times

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-
bounces@xxxxxxxxxxxx] On Behalf Of Luis Rodriguez
Sent: Thursday, December 16, 2010 3:54 PM
To: RPG programming on the IBM i / System i
Subject: Re: Problem using tlookup bif

Dennis,

This problem has piqued my curiosity, as LOOKUP is a opcode that I have
not
used in a (very) long time. I found this in a Bob Cozzi article (
http://systeminetwork.com/article/built-functions-you-might-not-be-
using-fully
)
:

"One thing that needs to be pointed out is that the %LOOKUP built-in
function performs a different routine to search the array than does the
legacy LOOKUP opcode. So there is a chance you could get a different
result
if you blindly convert LOOKUP opcodes to %LOOKUP built-in functions.

LOOKUP generated a subroutine based on the Resulting Indicators and
performed a sort of linear scan to locate matching elements,
whereas %LOOKUP
uses a binary search routine to find the elements. This means that if
the
data is not sequenced, %LOOKUP could fail to locate the elements even
if
they exist."

I wonder if David found a solution to his problem?

Regards,


Luis Rodriguez
IBM Certified Systems Expert - eServer i5 iSeries
--



On Thu, Dec 16, 2010 at 1:59 PM, Dennis Lovelady
<iseries@xxxxxxxxxxxx>wrote:

Yes. So that would be relevant if David were using %TLOOKUPxx. But

he's

not. He's using the %TLOOKUP, which does not use binary search.

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
"A fanatic is one who can't change his mind and won't change the

subject."

-- Winston Churchill

It looks to me like %TLOOKUPxx uses a binary search, as %lookupxx

does.

"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. "


On 12/16/2010 10:23 AM, Dennis Lovelady wrote:

The manual refers to both kinds of lookups. The kind that David

is

using is

not of the %TLOOKUPxx set, the nearest I can determine.

The %TLOOKUP

BIF

works by comparing each value starting with 1 and ending when a

match

is

found or the end of the table is reached. Sequence is immaterial.

Or at

least that's the way it was the first 35 years or so of the

language.

Dennis Lovelady
http://www.linkedin.com/in/dennislovelady
--
"A diplomat is a person who can tell you to go to hell in such a

way

that

you actually look forward to the trip."
-- Caskie Stinnett

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