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How do I get elements of a hash whose keys match a given regex?

alferic
Novice

Oct 2, 2013, 6:46 AM

Post #1 of 5 (3002 views)

How do I get elements of a hash whose keys match a given regex?	Can't Post

How do I get elements of a hash whose keys match a given regex?

I tried below script but it will not display the value.

my %hash = (
king => 1 ,
queen => 2,
);
my $regex =~ /queen/;

if (grep {/$regex/} keys %hash)
{
print "value is: $hash{$_}\n";
}
else
{
print "not found..\n";
}

FishMonger
Veteran / Moderator

Oct 2, 2013, 10:38 AM

Post #2 of 5 (2991 views)

Re: [alferic] How do I get elements of a hash whose keys match a given regex? [In reply to]	Can't Post

Tie::Hash::Regex - Match hash keys using Regular Expressions
http://search.cpan.org/~davecross/Tie-Hash-Regex-1.02/lib/Tie/Hash/Regex.pm

2teez
Novice

Oct 2, 2013, 10:41 AM

Post #3 of 5 (2991 views)

Re: [alferic] How do I get elements of a hash whose keys match a given regex? [In reply to]	Can't Post

You can do like thus:

Code

use strict; 
use warnings; 
 
my %hash = (  
king => 1 ,  
queen => 2,  
);  
 
 my $given_regex = qr/queen/; ## NOTE THIS 
 ## use a map 
 
   print map{$hash{$_},$/ if/$given_regex/} keys %hash; 
 
 ## use a for loop 
 
   for(keys %hash){ 
     print $hash{$_},$/ if /$given_regex/; 
   }

Laurent_R
Veteran / Moderator

Oct 3, 2013, 10:43 AM

Post #4 of 5 (2981 views)

Re: [alferic] How do I get elements of a hash whose keys match a given regex? [In reply to]	Can't Post

Just as an additional information on the errors in your code, you don't quite understand the grep syntax.

The grep function takes a list of values on its right and passes on its left the values for which the grep block returned true.

Second point, your $regex is not initialized correctly, you should use the assignment operator, not the match operator for that.

So you could have done this:

Code

my $regex = qr/queen/;  
my @matching_keys = grep {/$regex/} keys %hash;

Now, the @matching_keys array contains the values which matched the regex (just one, queen, in your case).

alferic
Novice

Oct 4, 2013, 6:10 AM

Post #5 of 5 (2975 views)

Re: [Laurent_R] How do I get elements of a hash whose keys match a given regex? [In reply to]	Can't Post

Thanks Gurus for the advises! I experimented and able to get what I want:
my %hash = (
king => 1 ,
queen => 2,
);
my $value ="";

my ($matching_key) = grep { $_ =~ /queen/ } keys %hash;

$value = $hash{$matching_key};

print "$value\n";

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