Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!iwarp.intel.com!news
From: merlyn@iwarp.intel.com (Randal Schwartz)
Newsgroups: comp.lang.perl
Subject: Re: Efficiency of eval (emulating multidimentional arrays)
Message-ID: <1990Jul5.171801.3176@iwarp.intel.com>
Date: 5 Jul 90 17:18:01 GMT
References: <13041@cbmvax.commodore.com>
Sender: news@iwarp.intel.com
Reply-To: merlyn@iwarp.intel.com (Randal Schwartz)
Distribution: comp.lang.perl
Organization: Stonehenge; netaccess via Intel, Beaverton, Oregon, USA
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In-Reply-To: schmid@spica.cbmvax.cbm.commodore.com (Bob Schmid)

In article <13041@cbmvax.commodore.com>, schmid@spica (Bob Schmid) writes:
| I'm using eval to create a large number of associative arrays based on
| different, variable dependent, names.  Eval seems to take about 1
| millisecond extra per eval on a Sparcstation1 compared with explicitly
| typing out the variable names.  This seems to me like a good tradeoff
| between execution speed and manageable coding complexity (I really
| need that extra array index!).
| 
| Any comments on eval efficiency or better ways to skin the cat will be
| most appreciated....
| 
| The following sample program uses integer indexing.  I usually use
| strings (hence the need for associative arrays).
| 
| for $cell (1..100)
| {
|     for $i (1..100)
|     {
| 	eval("\$junk_$cell{\$i} = \$i");
|     }
| }
| for $cell (1..100)
| {
|     while (($key, $val) = eval("each \%junk_$cell"))
|     {
|         print "\$key=$key \$val=$val";
|     }
| }

Do you *really* need all of those as separate variables?

I prefer things like:

for $cell (1..10) {
	for $i (1..10) {
		$data{"$cell $i"} = $i;
	}
}

for $cell (1..10) {
	for $key (sort grep(/^$cell /,keys data)) {
		print "$key = $data{$key}\n";
	}
}

If you don't care to access them by group, leave the 'grep' out.

Actually, I don't know which is more efficient.  Larry could probably
wake me up on this one (as usual).  What we're comparing is the speed
of parsing a string, and looking up something in the symbol table,
with looking up a hashed key in an assoc array.  I would think that
the second beats the first.  But intuition is a funny thing.

$_="cker,rl haer PeanothJust ";1 while s/(.{5})(.{5})?/$_{$2}=$1,$2/e;print while $_=$_{$_};
-- 
/=Randal L. Schwartz, Stonehenge Consulting Services (503)777-0095 ==========\
| on contract to Intel's iWarp project, Beaverton, Oregon, USA, Sol III      |
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