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Re^2: Hash value sorting

by iHutch105 (Initiate)
on Aug 14, 2012 at 12:26 UTC ( #987342=note: print w/ replies, xml ) Need Help??


in reply to Re: Hash value sorting
in thread Hash value sorting

Awesome, sorted with one minor adjustment to your code; I had to dereference the conditions of the sort because it was sorting by the scalar reference address. I changed it to:

foreach my $key ( sort { ${$self->{_counts}{$a}} <=> ${$self->{_counts}{$b}} } keys %{ $self->{_counts} }

Thanks so much for the help.


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Re^3: Hash value sorting
by greengaroo (Hermit) on Aug 14, 2012 at 12:57 UTC

    Try this:

    foreach my $key ( sort { $self->{_counts}->{$a} <=> $self->{_counts}->{$b} } keys %{ $self->{_counts} }

    If you do $self->{_counts}{$b}, Perl thinks $self->{_counts} is a real Hash, not an HashRef. If you use the arrow to dereference, it is easier to read.

    Take my advice. I don't use it anyway.
Re^3: Hash value sorting
by daxim (Chaplain) on Aug 14, 2012 at 13:44 UTC
    That code collides with your explanation of the data structure in 987336. Only one can be correct.

    In the constructor I see you initialise the field _counts with a hash reference. Where do you now get a scalar reference from?

    It would help if you dump $self before sorting, so we can see what the data structure really looks like.

    use Data::Dumper; print Dumper $self;

      You're absolutely right and I've found the problem.

      I made a mistake whenever I was creating/adding to values in the hash. I had this line:

      ${$self->{_counts}{$key}} += $value;

      This was where the scalar ref was coming from. I should note, key and value are parameter passed in, representing the obvious. This line explains why I had to do some extra, dodgy dereferencing later on and, of course, should have read:

      $self->{_counts}{$key} += $value;

      All seems to be sorted now. Code looks a lot tidier too. First time I've really used references much but it's been a good learning experience.

      Thanks to all for the help and suggestions.

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