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Perl: Any quick way to use regex on hash keys?

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# 1  
Old 06-10-2010
Perl: Any quick way to use regex on hash keys?
Hi,

Is there any quick way to use pull out keys that match a specific regex pattern?

eg
Code:
%hash ;
$hash(123,456) = xxx;
$hash(123,457) = xxx;
$hash(123,458) = xxx;
$hash(223,459) = xxx;

I need a fast way to get all the keys that start with 123..
Meaning I should get
Code:
$hash(123,456) = xxx;
$hash(123,457) = xxx;
$hash(123,458) = xxx;

only....

Currently I am looking through all the keys and using regex on them. I have over 2k such keys and it is making my program very slow. I am trying to tune it. Any suggestions are welcomed. Thank you.
Last edited by Leion; 06-10-2010 at 02:44 AM..
# 2  
Old 06-10-2010
Quote:
Originally Posted by Leion
...
Currently I am looking through all the keys and using regex on them. I have over 2k such keys and it is making my program very slow. ...
Can you post your code that does this ?

tyler_durden
# 3  
Old 06-10-2010
Here is the code...

Code:
 foreach $errBillkey(keys %hash)
 {
         if($errBillkey =~ m/^$account_no,.*/ )
        {
              // do something here
       }
}

# 4  
Old 06-10-2010
That looks quite okay. I tested out a similar logic with 7000 keys, and the time taken to create the hash + match + print is less than 1 second.

Code:
$ time perl -le 'BEGIN{$p="123"} foreach (120000..127000){$x{$_} = "xyz"} foreach $k(keys %x){if ($k =~ m/^$p.*/){print $k}}'
123223
123696
123691
...
...
123322
123712
123719

real    0m0.106s
user    0m0.048s
sys    0m0.019s
$

Maybe the bulk of the time is spent in the "do something" part ?

tyler_durden
# 5  
Old 06-10-2010
This could be a bit faster:
Code:
foreach $errBillkey(grep { /^$account_no/} keys %hash)

Unless you have to, don't try to match beyond the criteria. If it's still slow, you might want break down the hash a bit more, eg by creating a hash of hashes, where the keys of the first hash are the digits left of the comma.
# 6  
Old 06-10-2010
Thanks pludi and durden_tyler for helping to look at my issue.
I think the issue has been settled with pludi's suggestion. I will look into changing the code with hash of hash when i have time Smilie
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