perl sort issue while going through article at perl.com

convenientstore has asked for the wisdom of the Perl Monks concerning the following question:

what is wrong with below? I was going through tutorial in perl.com and first I think it has typo where it compares b to b (where it should be a to b and b to a) but also when I run the code itself, it does NOT sort it correctly..
Can you please tell me why this code does not sort it correctly?

http://www.perl.com/pub/a/2006/11/02/all-about-hashes.html



#!/usr/bin/perl -w

use strict;

my @list = qw(oranges oranges apple tomato tomato tomato tomato waterm
+elon watermelon watermelon);

my %histogram;
$histogram{$_}++ for @list;

my @unique = keys %histogram;

foreach (keys %histogram) {
  print "$_ ,  $histogram{$_}\n";
}


my @popular = (sort { $histogram{$b} <=> $histogram{$a} }  @unique)[0.
+.2];

print "@popular\n";

__END__
foreach (keys %histogram) {
  print "$_ ,  $histogram{$_}\n";
}
[root@myserver chaos]# ./!$
./perl.hashcrashcourse
oranges ,  2
watermelon ,  3
tomato ,  4
apple ,  1
tomato watermelon oranges




#!/usr/bin/perl -w

use strict;

my @list = qw(oranges oranges apple tomato tomato tomato tomato waterm
+elon watermelon watermelon);

my %histogram;
$histogram{$_}++ for @list;

my @unique = keys %histogram;

foreach (keys %histogram) {
  print "$_ ,  $histogram{$_}\n";
}


my @popular = (sort { $histogram{$a} <=> $histogram{$b} }  @unique)[0.
+.2];

print "@popular\n";

__END__
foreach (keys %histogram) {
  print "$_ ,  $histogram{$_}\n";
}
[root@myserver chaos]# ./!$
././perl.hashcrashcourse
oranges ,  2
watermelon ,  3
tomato ,  4
apple ,  1
apple oranges watermelon
[download]

Comment on perl sort issue while going through article at perl.com Download Code

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Re: perl sort issue while going through article at perl.com by shmem (Chancellor) on Oct 21, 2007 at 18:22 UTC
`my @popular = (sort { $histogram{$b} <=> $histogram{$a} } @unique)[0. +.2]; print "@popular\n"; __END__ tomato watermelon oranges` [download] Correct - hash keys, sorted descending by value, first three ( values are 4,3,2). `my @popular = (sort { $histogram{$a} <=> $histogram{$b} } @unique)[0. +.2]; print "@popular\n"; __END__ apple oranges watermelon` [download] Also correct - hash keys, sorted ascending by value, first three (values are 1,2,3). If you iterate over the hash keys and print them out with their value, they will come out in any order. A hash isn't sorted. --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^2: perl sort issue while going through article at perl.com by convenientstore (Pilgrim) on Oct 22, 2007 at 05:18 UTC
one more question from same tutorial, can you do below in reference hash? `my %histogram; $histogram{$_}++ for @list;` [download] I was trying `foreach (@data1) { $hist{$_}++ for $_; } my @uni = keys %hist; print "@uni\n";` [download] but above actually prints out the reference address. I tried few different things but does not print out the actual value.. can someone give me a pointer on this(no pun intended).. thanks. for example like below.... `#!/usr/bin/perl -w use strict; use warnings; use Data::Dumper; my $ref = { a => { A => 1, B => 2, C => 3}, b => { D => 1, E => 2, F => 4}, c => { G => 2, H => 1, I => 2}, }; #print Dumper($ref); my %hist; foreach ($ref) { $hist{$_}++ for $_; } my @uni = keys %hist; print "@uni\n";` [download]	[reply] [d/l] [select]
Re^3: perl sort issue while going through article at perl.com by shmem (Chancellor) on Oct 22, 2007 at 08:16 UTC
`foreach ($ref) { $hist{$_}++ for $_; }` [download] Your `$ref` is a hash reference - use keys: `for ( keys %$ref) { ... }` [download] Since your data structure is a HoH, inside that loop `$_` is, again, a hash reference. Again you need keys. `$hist{$_}++ for keys %$_;` [download] But such usage of `$_` is a bit obfuscated. Better say `for my $hashref ( keys %$ref) { $hist{$_}++ for keys %$hashref; }` [download] --shmem _($_=" "x(1<<5)."?\n".q·/)Oo. G°\ / /\_¯/(q / ---------------------------- \__(m.====·.(_("always off the crowd"))."· ");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}	[reply] [d/l] [select]
Re^4: perl sort issue while going through article at perl.com by convenientstore (Pilgrim) on Oct 22, 2007 at 14:55 UTC
Re^4: perl sort issue while going through article at perl.com by convenientstore (Pilgrim) on Oct 23, 2007 at 00:30 UTC
Re^5: perl sort issue while going through article at perl.com by shmem (Chancellor) on Oct 23, 2007 at 05:51 UTC
Re^5: perl sort issue while going through article at perl.com by convenientstore (Pilgrim) on Oct 23, 2007 at 22:14 UTC
Some notes below your chosen depth have not been shown here
Re: perl sort issue while going through article at perl.com by duff (Parson) on Oct 21, 2007 at 17:59 UTC
Er, how does it not sort correctly? If I'm missing something obvious, please highlight it for me. duff	[reply]
Re^2: perl sort issue while going through article at perl.com by convenientstore (Pilgrim) on Oct 21, 2007 at 18:16 UTC
you are right. I was thinking that it should have been oranges, watermelon, tomato instead apple, oranges, watermelon stupid thinking... my bad.. thanks for pointing this out	[reply]