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From: markb@agora.uucp (Mark Biggar)
Newsgroups: comp.lang.perl
Subject: Re: The best way to search an array ?
Keywords: detab
Message-ID: <1990Dec3.035541.24184@agora.uucp>
Date: 3 Dec 90 03:55:41 GMT
References: <443@stephsf.stephsf.com>
Organization: Open Communications Forum
Lines: 65

In article <443@stephsf.stephsf.com> wengland@stephsf.stephsf.com (Bill England) writes:
>
>  What is the best method for discovering if a string is in
>  a given set of strings?  For example say you want to verify
>  that the string 'WA' is a valid two char state abreviation?
>
>  I can think of at least four methods ...
>
>  Method      Description
>
>    1       Search a string that contains all two letter state names;
>            Here you would prefix and suffix the state var and
>            then search the string.  Something like ;
>			...
>			$state = '~AK~AL~AR~AZ~CA~CO~...';
>			$search_string = '~'.$prove_state.'~';
>            if( /$search_string/ eq $state) { ... }
>
If you search set is small this may be the bets way, but use index() instead of
of an regular expression, like so:

	     if (index($state, "~$prove_state~") > = 0)

Besides your if condition is wrong, it should be:

	     if ($state =~ /~$prove_state~/)

>    2       Build an associative array %state so that you have;
>            $state{'AK'}="Alaska";
>            $state{'AL'}="Alabama";
>            $state{'AR'}="Arkansas";
>            $state{'AZ'}="Arizona";
>            $state{'CA'}="California";
>            ...
>            Then test for the existance of $state{$prove_state}.
>            ( Has disadvantage of extra bagage if you don't need the
>              states full name.   )
>
if you don't need the full names just set the associated array value to 1.
this is a very good way to go if the search set is generated by your
program.  If you have a very large constant search set using a dbm file
for it may be the best way to go.

>    3       Build a simple array and then search with a foreach
>                @state = ('AK','AL','AR','AZ','CA', ...);
>                foreach $st(@state){
>                    last if $st eq $prove_state;
>                }
>
This is only good if you need the array for other reasons, such as an array
of month names that you wish to index by month number.

>    4       The same as 3 above but, use a binary search instead of
>            a linear search.
>
Same problems as with 3.

>   Which of the above would be the best to use in perl? 
>
>   Is there a better way ???

That pretty much covers it.
--
Perl's maternal uncle
Mark Biggar


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