Using regex to extract keys

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

Dear all,

I have a large hash where every key in the hash is of the format:\w\d\d, and I want to use keys to extract an array of keys that match any \d\d pattern, (hence ignoring letters) like so:

my $r = 44;
foreach my $key (keys %{$self->{'residues'}{$modelCount}{/^\w$r$/}}){
        print $key."\n";
}
[download]

This doesnt work as it is, but is there a possible solution, or should I just step through the keys ahd store an array of the ones that match?

Cheers
Sam

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Re: Using regex to extract keys by perlmonkey (Hermit) on Sep 24, 2003 at 20:59 UTC
use grep: `my $r = 44; my $hash = $self->{'residues'}{$modelCount}; for my $key ( grep { /^\w$r$/ } keys %$hash ) { print $key."\n"; }` [download] Update:Yup, as abigail suggested use each for large hashes so you dont duplicate the memory needed for the keys: `my $r = 44; my $hash = $self->{'residues'}{$modelCount}; while( my ($key, $value) = each %$hash ) { next if $key =~ /^\w$r$/; print $key."\n"; }` [download]	[reply] [d/l] [select]
Re: Using regex to extract keys by Abigail-II (Bishop) on Sep 24, 2003 at 21:17 UTC
Since the hash is given to be large, one might prefer iterating over the hash using `each` in a `while` loop. In the loop, test whether the key matches /^\w$r$/. If not, do a `next`. Abigail	[reply]
Re: Re: Using regex to extract keys by seaver (Pilgrim) on Sep 25, 2003 at 13:59 UTC
Fantastic, Thanks! I was disappointed because I was hoping that there was some inherent regex in calling a hash key, but obviously I cant do it that way. The while loop with each does the job just grand. Cheers Sam	[reply]
Re: Using regex to extract keys by Mr. Muskrat (Canon) on Sep 24, 2003 at 20:59 UTC
Get your keys and check for matches. `my %hash = ( a44 => 'aha!', b33 => 'boo!', c45 => 'close.', d44 => 'aha!', e44 => 'aha!', f46 => 'too far...', ); my $r = 44; foreach my $key (keys %hash){ print $key."\n" if $key =~ /\w$r/; } __DATA__ e44 a44 d44` [download]	[reply] [d/l]

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