RE: Bsearch for closest match

Thanks Scott.  

For the example that I've (which you mentioned that it could be elem 2,3
or,4), is there a pattern on which elem it will pick?

If this array is a physical file and I did a setll and then readp, I
would expect it to always pick elem 4.

-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx
[mailto:rpg400-l-bounces@xxxxxxxxxxxx] On Behalf Of Scott Klement
Sent: Monday, August 21, 2006 5:53 PM
To: RPG programming on the AS400 / iSeries
Subject: Re: Bsearch for closest match


Bsearch() has to find an exact match on something.  It can find an exact
match on PART of your key, but, some part of it must match exactly.

In your example, you have this:

Array(1) = 'AB'
Array(2) = 'ABC'
Array(3) = 'ABCD'
Array(4) = 'ABCDEF'
Array(5) = 'ACCDEF'

Search key is ABCE123.

For this example, you could search for the first 3 letters (ABC) to
match. 
When you found a match (which could be any of elemnts 2, 3 or 4) you
could then read backward and forward in the array to find the "closest"
match.

However, what if you had this?

Array(1) = AAAAAAA
Array(2) = BBBBBBB
Array(3) = CCCCCCC
Array(4) = FFFFFFF
Array(5) = GGGGGGG
Array(6) = HHHHHHH

Search key is DEFGHIJ

In this case, I'd think you'd want #4 to be the "closest match" (sort
of, I guess) since it's the next higher element.  But you can't do that
with
bsearch() because there's no part of the element that matches exactly.

Instead of using bsearch(), you might be better off writing your own
binary search tool.  It would do this:

a) Array has 6 elements... so check element 3.
b) Is key > element 3?  Yes.  We have elemnts 4,5,6 left, so try 5.
c) Is key > element 5?  No.
d) IS key < element 5?  YEs.  We have element 4 left.
e) Is key < element 4?  Yes.  Is key > element 3?  Yes. Closest match is
element 4.

Something like that...

--
Scott Klement  http://www.scottklement.com

On Mon, 21 Aug 2006, Lim Hock-Chai wrote:

I've a dynamic array that I need to do bsearch with closest prefix 
matched element. Does anybody has an example on how to that?

Eample:
Array(1) = 'AB'
Array(2) = 'ABC'
Array(3) = 'ABCD'
Array(4) = 'ABCDEF'
Array(5) = 'ACCDEF'

if search argument is ABCE123 ==> The closest match would be elem 2.

thanks.

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