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RE: sort order of hash keys

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From:
John Edwards
Date:
February 26, 2002 02:33
Subject:
RE: sort order of hash keys
Message ID:
2FB59B145095D511A7C90050BAC349F31732AC@MAIL
hash keys are stored unsorted. If you have the following hash

%test = (	one => 1,
		two => 2,
		three => 3);

and print out the hash key/value pairs.

foreach $key (keys %test) {
	print "$key is $test{$key}\n";
}

you will find they don't come out in the same order as they were stored.

You can perform a sort on the keys to arrange them in order

foreach $key (sort keys %test) {
	print "$key is $test{$key}\n";
}

or you can reverse the hash, making the values the keys, and sort on the new
keys

%reversed = reverse %test;

foreach $key (keys %reversed) {
	print "$key is $reversed{$key}\n";
}

In doing this though, you must be aware that you will lose any data that has
identical values. For example

%test = (	one => 1,
		two => 2,
		three => 3,
		alpha => 1,
		beta => 2,
		gamma => 3);

%reversed = reverse %test;

foreach $key (keys %reversed) {
	print "$key is $reversed{$key}\n";
}

will print out

1 is one
2 is two
3 is three

There is probably another/better way of doing this using the comparison
operator <=>, but I don't know it. There is also a module available that
lets you store and retrieve hashes in a fixed order.
-----Original Message-----
From: maasha@image.dk [mailto:maasha@image.dk]
Sent: 26 February 2002 09:16
To: beginners@perl.org
Subject: sort order of hash keys


hi


i would like to know if theres a smart way to unwind a hashtable so that
the key / value pairs comes out in the same order as they are in the table.

:o)

martin
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