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From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: assoc array
Keywords: assoc array, keys, order
Message-ID: <1991May18.160757.15011@convex.com>
Date: 18 May 91 16:07:57 GMT
References: <5102@syma.sussex.ac.uk>
Sender: usenet@convex.com (news access account)
Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
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Nntp-Posting-Host: pixel.convex.com

From the keyboard of sylvank@syma.sussex.ac.uk (Sylvan Katz):
:I have an application which requires that I initialize an associative
:array for counting purposes:
:
:EG:
:
:	%matrix = ('A',0,'AA',0,'B',0,'BB',0);
:
:However, when I examine the order of the array elements with
:
:	foreach $key (keys %matrix) { print "$key ";}
:
:I find order is
:
:	BB A B AA 
:
:Any suggestions on how I can PRESERVE the initial order (it is
:imperative for my applications) ?

If you're not adding any elements to the array, you could do this:

    @keys = ('A','AA','B','BB');
    @matrix{@keys} = ();

or, if having the values initialized to undef bothers you:

    @matrix{@keys} = (0) x @keys;

Then process them with:

    for $key (@keys) {
	print "key ", $key, " is ", $matrix{$key}, "\n";
    } 

Other more baroque ideas come to mind, like this one, which might
perhaps be of use to you if you have some other criteria I'm
not aware of:

    %order = (); $order = 0;
    for (@keys) { $order{$_} = $order++; } 
    # later on...
    sub by_order { $order{$a} <=> $order{$b}; }
    for (sort by_order keys %matrix) {
	print "key ", $key, " is ", $matrix{$key}, "\n";
    } 

In short, it all else fails, call an auxiliary function to help you
get the ordering down.


--tom
--
Tom Christiansen		tchrist@convex.com	convex!tchrist
		"So much mail, so little time."