Re^2: Regex with variables

If there are numerous lookups, I agree, but if it's just a couple of quick lookups, that's not necessarily true. To extract the string into a hash seems to take significantly longer than just a straight regex lookup:

#!/usr/bin/perl

use warnings;
use strict;

use Benchmark qw(:all);

cmpthese ( 5000000, {
                'string' => 'string()',
                'hash' => 'hash()',
            });

sub string {
    my $str = "1689 9679 2792 2514 5472 1520 9342 5544 1268 0165 1979 
+7314 2101 7221 9539 3882 1812";
    my $test = 2101;
    if ($str =~ $test){
        # do stuff
    }
}
sub hash {
    my $str = "1689 9679 2792 2514 5472 1520 9342 5544 1268 0165 1979 
+7314 2101 7221 9539 3882 1812";
    my $test = 2101;
    my %hash;
    for (split /\s+/, $str){
        $hash{$_}++;
    }
    if (exists $hash{$test}){
        # do stuff
    }
}

__END__
            Rate   hash string
hash    267237/s     --   -92%
string 3521127/s  1218%     --
[download]

Comment on Re^2: Regex with variables Download Code

Replies are listed 'Best First'.
Re^3: Regex with variables by 1nickt (Canon) on Jun 29, 2015 at 14:37 UTC
Hi Stevieb, I wasn't considering performance but rather the ease of maintenance of a list of items. The OP has `$targets` (plural) as the name of his string, so I assumed that at some point he had a list, and then put it into a string. I agree that if he originally had a string like that (e.g. from a log file) then a regexp would be the way to find a substring of it. But if he has a list then putting it into a string and looking for a match is headed in the wrong direction, IMO. Update: I wanted to know, so now I do. In this case join()ing the list into a string and then using a regexp is still much faster than populating a hash: `use Benchmark qw(:all); cmpthese ( 5000000, { 'string' => 'string()', 'hash' => 'hash()', 'list2string' => 'list2string()', }); # other subs as before sub list2string { my $str = join( ' ', qw/1689 9679 2792 2514 5472 1520 9342 5544 1268 + 0165 1979 7314 2101 7221 9539 3882 1812/ ); my $test = 2101; if ($str =~ $test){ # do stuff } } __END__ Rate hash list2string st +ring hash 62406/s -- -88% +-95% list2string 530223/s 750% -- +-61% string 1355014/s 2071% 156% + --` [download] But I still wouldn't do it myself as combining discrete values into a string just feels wrong.	[reply] [d/l] [select]
Re^4: Regex with variables by stevieb (Canon) on Jun 29, 2015 at 15:21 UTC
If the OP's data was indeed in a list, I'd probably opt for grep(), `if grep(/$test/, @list)...`. The good thing about Perl, is TIMTOWTDI ;)	[reply] [d/l]