perl sort issue while going through article at perl.com

[convenientstore]

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

[shmem]

my @popular = (sort { $histogram{$b} <=> $histogram{$a} }  @unique)[0.
+.2];
print "@popular\n";
__END__
tomato watermelon oranges

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

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.

[convenientstore]

one more question from same tutorial, can you do below in reference hash?

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

I was trying

foreach (@data1) {
      $hist{$_}++ for $_;
}

my @uni = keys %hist;

print "@uni\n";

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";

[shmem]

foreach ($ref) {
    $hist{$_}++ for $_;
}

Your $ref is a hash reference - use keys:

for ( keys %$ref) {
    ...
}

Since your data structure is a HoH, inside that loop $_ is, again, a hash reference. Again you need keys.

    $hist{$_}++ for keys %$_;

But such usage of $_ is a bit obfuscated. Better say

for my $hashref ( keys %$ref) {
    $hist{$_}++ for keys %$hashref;
}

[duff]

Er, how does it not sort correctly? If I'm missing something obvious, please highlight it for me.

[convenientstore]

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