Re^2: are they all there?

Nice, but instead of compiling {number of collections} * {number of required items} regexps, swap your loops to only compile {number of required items} regexps.

foreach my $item ( @required ) {
  foreach my $collection ( @collections ) {
    $collection .= " $item" unless $collection =~ /\b$item\b/;
  }
}
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Comment on Re^2: are they all there? Download Code

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Re^3: are they all there? by ikegami (Patriarch) on Aug 23, 2006 at 19:24 UTC
I was asked How do we know that perl is smart enough not to recompile the regexp with every iteration of the inner loop nonetheless? We can use `use re 'debug';` to see the difference. `use re 'debug'; for my $i (1..2) { for my $re (qw( abc def )) { $i =~ /$re/; } }` [download] ouputs Compiling REx `abc' <------------ size 3 first at 1 1: EXACT <abc>(3) 3: END(0) anchored `abc' at 0 (checking anchored isall) minlen 3 Freeing REx: `abc' Compiling REx `def' <------------ size 3 first at 1 1: EXACT <def>(3) 3: END(0) anchored `def' at 0 (checking anchored isall) minlen 3 Freeing REx: `def' Compiling REx `abc' <------------ size 3 first at 1 1: EXACT <abc>(3) 3: END(0) anchored `abc' at 0 (checking anchored isall) minlen 3 Freeing REx: `abc' Compiling REx `def' <------------ size 3 first at 1 1: EXACT <def>(3) 3: END(0) anchored `def' at 0 (checking anchored isall) minlen 3 Freeing REx: `def' [download] while `use re 'debug'; for my $re (qw( abc def )) { for my $i (1..2) { $i =~ /$re/; } }` [download] outputs Compiling REx `abc' <------------ size 3 first at 1 1: EXACT <abc>(3) 3: END(0) anchored `abc' at 0 (checking anchored isall) minlen 3 Freeing REx: `abc' Compiling REx `def' <------------ size 3 first at 1 1: EXACT <def>(3) 3: END(0) anchored `def' at 0 (checking anchored isall) minlen 3 Freeing REx: `def' [download] If the interpolated variables are still the same as they were the last time the regexp was compiled, the regexp is not recompiled. Update: We get the same results with `/\b$re\b/`.	[reply] [d/l] [select]

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Re^3: are they all there?
by ikegami (Patriarch) on Aug 23, 2006 at 19:24 UTC

I was asked

How do we know that perl is smart enough not to recompile the regexp with every iteration of the inner loop nonetheless?

We can use use re 'debug'; to see the difference.

use re 'debug';

for my $i (1..2) {
   for my $re (qw( abc def )) {
      $i =~ /$re/;
   }
}
[download]

ouputs

Compiling REx `abc'         <------------
size 3 first at 1
   1: EXACT <abc>(3)
   3: END(0)
anchored `abc' at 0 (checking anchored isall) minlen 3 
Freeing REx: `abc'
Compiling REx `def'         <------------
size 3 first at 1
   1: EXACT <def>(3)
   3: END(0)
anchored `def' at 0 (checking anchored isall) minlen 3 
Freeing REx: `def'
Compiling REx `abc'         <------------
size 3 first at 1
   1: EXACT <abc>(3)
   3: END(0)
anchored `abc' at 0 (checking anchored isall) minlen 3 
Freeing REx: `abc'
Compiling REx `def'         <------------
size 3 first at 1
   1: EXACT <def>(3)
   3: END(0)
anchored `def' at 0 (checking anchored isall) minlen 3 
Freeing REx: `def'
[download]

while

use re 'debug';

for my $re (qw( abc def )) {
   for my $i (1..2) {
      $i =~ /$re/;
   }
}
[download]

outputs

Compiling REx `abc'         <------------
size 3 first at 1
   1: EXACT <abc>(3)
   3: END(0)
anchored `abc' at 0 (checking anchored isall) minlen 3 
Freeing REx: `abc'
Compiling REx `def'         <------------
size 3 first at 1
   1: EXACT <def>(3)
   3: END(0)
anchored `def' at 0 (checking anchored isall) minlen 3 
Freeing REx: `def'
[download]

If the interpolated variables are still the same as they were the last time the regexp was compiled, the regexp is not recompiled.

Update: We get the same results with /\b$re\b/.

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