Re: grep value in hash

Depends what exactly you need to do.

If you just want to know if the value is in the has then you can use values.

if (grep { $_ eq '111' } values %hash) {
  print 'found';
}
[download]

If you want to know which key is associated with the value, you can use keys.

foreach (keys %hash) {
  if ($hash{$_} eq '111') {
    print "Found at key $_";
    last;
  }
}
[download]

Or each.

while (my ($k, $v) = each %hash) {
  if ($v eq '111') {
    print "Found at key $k";
    last;
  }
}
[download]

--
<http://dave.org.uk>

"The first rule of Perl club is you do not talk about Perl club."
-- Chip Salzenberg

Comment on Re: grep value in hash Select or Download Code

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Re^2: grep value in hash by Fletch (Bishop) on Feb 17, 2006 at 13:13 UTC
Alternately if this is something you need to do often build an inverted hash with the keys and values switched. `my %hash_inverted; @hash_inverted{ values %hash } = keys %hash;` [download] Just remember that this won't be automagically updated so if you update `%hash` you'll need to also update `%hash_inverted` (and/or wrap them both up in an object and let that keep things updated for you when you use its accessors). Update: Good point below about duplicates, which also brings up the point that if your original hash has non-scalar values you may need something like Tie::RefHash for the inverted version.	[reply] [d/l] [select]
Re^3: grep value in hash by revdiablo (Prior) on Feb 17, 2006 at 16:43 UTC
Another issue to be aware of is duplicate values. This can be handled by doing a bit more work with the inversion: `my %hash_inverted; for (keys %hash) { my $value = $hash{$_}; push @{ $hash_inverted{$value} }, $_; }` [download] This way each value in the inverted hash will be an array reference, which contains all the keys that value corresponds to.	[reply] [d/l]
Re^2: grep value in hash by Anonymous Monk on Dec 04, 2020 at 05:32 UTC
Hi, can you please give me insight about the code `grep { $_ eq '111' } values %hash`	[reply] [d/l]
Re^3: grep value in hash by eyepopslikeamosquito (Archbishop) on Dec 04, 2020 at 07:14 UTC
The node you're responding to is over 14 years old! Sadly, its celebrated author (the famous davorg) hasn't visited us for more than two years and so is unlikely to respond. BTW, davorg, aka Dave Cross, is former head honcho of London.pm (around the time they sponsored a camel at London zoo), professional Perl trainer for over twenty years, and the author of at least four Perl books. Let's hope he visits us again soon. Meanwhile, I'll try to explain his masterful one-liner for you. You should read the immortal line: `grep { $_ eq '111' } values %hash` [download] as a "pipeline" from right to left. The call to `values %hash` returns a list of all values in the hash (see values). The grep function evaluates the `{ $_ eq '111' }` code block for each element of this list (locally setting `$_` to each element), returning a list consisting of those elements for which the expression evaluated to true. That is, it returns a list of all values in `%hash` which have the exact value `111`. Note that hashes have unique keys but their values are not unique, so the list returned by this expression may have more than one element; the above expression will only tell you how many times the value `111` appears in the hash but will not tell you the keys of the hash with that value -- for that, you would need to iterate through the keys of the hash instead, checking each value in turn (as the legend davorg did in his second code snippet, using the keys function). Now I've answered your question, you gotta tell me why you were asking a question about such an ancient node (I won't be able to sleep tonight not knowing).	[reply] [d/l] [select]