From: Tim Hammerquist <penryu@...>
Date: 2005-12-10T07:04:57+09:00
Subject: Re: new to Ruby - pls help in translating this

Sam Dela Cruz <sam.dela.cruz@philips.com> wrote:
> I'm starting to use Ruby in one of my projects at work.  I'm
> coming from a Perl background.
> 
> In my project I would need to parse a list of numbers
> (thousands of them) and then return the duplicates.  In perl,
> I can do this:
>
> ##### Perl code
> %hash = {};

That doesn't do what you think it does.  In Perl, the {} here
will create a hash reference, which is a scalar datatype.
You're assigning it to a %hash variable, which accepts LIST
data.  This ends up being the same as:

  %hash = ( {} );

Which creates a hash named %hash, stringifies the hash reference
and uses it as a key, and without any additional values to work
with, uses undef as a value for the key.

To see this in action:

    use Data::Dumper;
    my %hash = {};
    print Dumper( \%hash );

Compare to:

    use Data::Dumper;
    my %hash = ();
    print Dumper( \%hash );

Yes. You want to use parentheses.

> while (<>)
> {
>     chomp;
>         $hash{$_}++;
> }
>
> foreach my $key (sort keys %hash)
> {
>     print "$key: $hash{$key}\n" if ($hash{$key} > 1);
> }


HTH,
Tim Hammerquist