[Perl-beginners] RE: An Old Question on Sorting Hash of Arrays by Array element an d th en by key

Perl uses its own internal storage method for Hashes.
There is no guarantee of order unless you sort it and
save the results yourself.


You need the key value to get the hash data.
Keys, in of themselves, are of little value.

First, did you catch the later post that pointed out my mistake?
Here's the corrected code:

my @ordered_keys = sort { $HofA{$a}[0] cmp $HofA{$b}[0]
$a cmp $b } keys %HofA;

Yes, I only ordered the keys. Sorry if I didn't make that clear.
That's all you need though, right? ;)

foreach (@ordered_keys) {
print "$HofA{$_}[0], $_, $HofA{$_}[1]\n";
}

Hope that helps.

James

%HofA = (orange=>['ZZZ', 'ANDY'],
red=>['AAA', 'AL'],
blue=>['mmm','Betty'],
yellow=>['aaa', 'ZEUS'],
green=>['DDD','Mary Joe'],
violet=>['MMM','Hugo']
);

my @ordered_keys = sort { $HofA{$a}[0] cmp $HofA{$b}[1]
$a cmp $b } keys %HofA;


foreach $value (@ordered_keys) { print "$value\n"; }


FYI:

Perl Cookbook - 5.4. Traversing a Hash

Problem -- You want to perform an action on each entry (i.e., each
key-value pair) in a hash.

Solution -- Use each with a while loop:

while(($key, $value) = each(%HASH)) {
# do something with $key and $value
}

Or use keys with a foreach loop, unless the hash is potentially very large:

foreach $key (keys %HASH) {
$value = $HASH{$key};
# do something with $key and $value
}

-Sx-

Hi Jeff.

James was offering you a starting place. The only way to order
a hash is to order its keys, hence 'my @ordered_keys'. What you
do with this sorted list depends on what you want. For instance

foreach (@ordered_keys) {
printf "%s => %s\n", $_, $HofA{$_};
}

Also, I wasn't sure whether, by
you meant that the string comparisons for the sort should be
case-insensitive. If so, then your sort should look like

my @ordered_keys = sort {
my ($aa, $bb) = lc $a, lc $b;
$HofA{$aa}[0] cmp $HofA{$bb}[0] or $aa cmp $bb
} keys %HofA;

HTH,

Rob

I really need to order both the keys and one of the elements in the array
stored as a value in the hash, preferably sort first on the first element of
the array (my real application has four elements but the snippet I'm testing
with has a two-element array) and then sort secondly on the key.

So if the reference to the array stored as the hash value is called
"$value", then there are two elements, $$value[0] and $$value[1], that it
references, right?
I want to sort first on $$value[0], then on the key for HofA, and to then be
able to print a report that lists all the data I need, including the two
sorted values plus also the other, non-sorted values stored in the HofA
array. That way the output is easier to read and summarize for the user.

Does this make sense? I know how to sort by keys but sort first by the
value element and then by keys is my block...

-----Original Message-----
From: James Edward Gray II
Sent: Thursday, February 19, 2004 11:37 AM
To: Smith Jeff D
Cc: '[email protected]'
Subject: Re: An Old Question on Sorting Hash of Arrays by Array element an d
th en by key

First, did you catch the later post that pointed out my mistake?
Here's the corrected code:

my @ordered_keys = sort { $HofA{$a}[0] cmp $HofA{$b}[0]
$a cmp $b } keys %HofA;

Yes, I only ordered the keys. Sorry if I didn't make that clear.
That's all you need though, right? ;)

foreach (@ordered_keys) {
print "$HofA{$_}[0], $_, $HofA{$_}[1]\n";
}

Hope that helps.

James

Research:

Tie::IxHash

Hi Jeff.

I was hoping James would be around, but, briefly:

A hash element is a key/value pair, but it is accessed uniquely
by its key. You can sort the elements on any function of the key,
the value, or both; but the result will be an ordered list of keys.

Does that help? I hope so!

Rob

Are you playing with the code I'm posting? :P

I know how you would like it sorted. I did that. (Actually, I believe
I did miss the case insensitive part, but Rob has already fixed that.)

A Perl hash is an unordered structure. However, if we put the keys in
the order we want and then use those to access the values, we're good
to go. I posted a loop showing this in my last message.

I ordered the keys based on the first value and the key itself, just
like you said. In order to avoid more confusion though, here's a proof
of concept:

#!/usr/bin/perl

use strict;
use warnings;

# create some data
my %HofA = ( orange => ['ZZZ', 'ANDY'],
red => ['AAA', 'AL'],
blue => ['mmm','Betty'],
yellow => ['aaa', 'ZEUS'],
green => ['DDD','Mary Joe'],
violet => ['MMM','Hugo'] );

# sort it
my @ordered_keys = sort { lc($HofA{$a}[0]) cmp lc($HofA{$b}[0])
lc($a) cmp lc($b) } keys %HofA;

# print it
foreach (@ordered_keys) {
print "$HofA{$_}[0], $_, $HofA{$_}[1]\n";
}

__END__

You'll notice that the above is really just a summary of this thread.
When I run it, I get:

AAA, red, AL
aaa, yellow, ZEUS
DDD, green, Mary Joe
mmm, blue, Betty
MMM, violet, Hugo
ZZZ, orange, ANDY

Which is the output you requested in your original message.

Hope that helps.

James

Thanks, I must have missed it--I'll be getting back to it tomorrow morning
to see what I missed in the original response. I thought I had run as
printed below.

Anyway, thank for the help...I think I may have braced when I should have
paren'd... It so simple when someone else does it first.... I was trying to
nest the sorts rather
than logically or'ing them together and it wasn't working.

-----Original Message-----
From: James Edward Gray II
Sent: Thursday, February 19, 2004 3:12 PM
To: Smith Jeff D
Cc: '[email protected]'
Subject: Re: An Old Question on Sorting Hash of Arrays by Array element an d
th en by key

Are you playing with the code I'm posting? :P

I know how you would like it sorted. I did that. (Actually, I believe
I did miss the case insensitive part, but Rob has already fixed that.)

A Perl hash is an unordered structure. However, if we put the keys in
the order we want and then use those to access the values, we're good
to go. I posted a loop showing this in my last message.

I ordered the keys based on the first value and the key itself, just
like you said. In order to avoid more confusion though, here's a proof
of concept:

#!/usr/bin/perl

use strict;
use warnings;

# create some data
my %HofA = ( orange => ['ZZZ', 'ANDY'],
red => ['AAA', 'AL'],
blue => ['mmm','Betty'],
yellow => ['aaa', 'ZEUS'],
green => ['DDD','Mary Joe'],
violet => ['MMM','Hugo'] );

# sort it
my @ordered_keys = sort { lc($HofA{$a}[0]) cmp lc($HofA{$b}[0])
lc($a) cmp lc($b) } keys
%HofA;

# print it
foreach (@ordered_keys) {
print "$HofA{$_}[0], $_, $HofA{$_}[1]\n";
}

__END__

You'll notice that the above is really just a summary of this thread.
When I run it, I get:

AAA, red, AL
aaa, yellow, ZEUS
DDD, green, Mary Joe
mmm, blue, Betty
MMM, violet, Hugo
ZZZ, orange, ANDY

Which is the output you requested in your original message.

Hope that helps.

James

No worries. You probably did run my original response, which was
flawed. Mark gave a fix for it shortly after I posted it. Then Rob
pointed out that it was ignoring your case insensitive request today.
All their suggestions are included below.

The Moral: Don't use the original message. Use this one.
Oring sort() conditions is a common Perl idiom. Now you know. ;)

James

Far more reliable is: "Don't do what I say, do what I mean." :)

Rob

After all, Perl is a DWIM language. :-)


John

Ooops. Bad things happen when you start out too quickly specifying program
structures. When you need an ordered array, you need to use an array, rather
than a hash. Hashes *do not, ever* offer any warranty on internal ordering.
What they offer instead is speedy access to string-keyed data elements.
I'm afraid your original thread got spearated from this post, so that is hard to
say. Usually, the way to control ordering of hash output is to sort on the
keys.

foreach (sort {$a <=> $b} keys %my_hash) { #numeric
foreach (sort {$a cmp $b} keys %my_hash) { #ASCII
foreach (sort {my_compare($a, $b)} keys %my_hash) { # custom comparison
do_things $my_hash{$_};
}

If there is a special ordering to the keys that cannot be expressed in a
standard comparison function, this might be an indication that you shoud be
using a package to hold the information, so that you can treat the data in the
specific ordering called for in its logical context..


Joseph

It's working fine and thanks for your help---hopefully my users will welcome
the difference.

Thanks again.

-----Original Message-----
From: James Edward Gray II
Sent: Thursday, February 19, 2004 4:42 PM
To: Smith Jeff D
Cc: '[email protected]'
Subject: Re: An Old Question on Sorting Hash of Arrays by Array element an d
th en by key

No worries. You probably did run my original response, which was
flawed. Mark gave a fix for it shortly after I posted it. Then Rob
pointed out that it was ignoring your case insensitive request today.
All their suggestions are included below.

The Moral: Don't use the original message. Use this one.
Oring sort() conditions is a common Perl idiom. Now you know. ;)

James