Re: How do I remove whitespace at the beginning or end of my string?

I wrote some benchmark code to test the popular answers, and a method using just pattern match and capture instead of s///. I got good results from my pattern match, so I tried plugging my pattern into Daddio's solution (s-capture), and got a significant speedup of it (s-capture2), but still not as good as just using m//.

use Benchmark 'cmpthese';
use Regexp::Common 'whitespace';

my $f = '   this is a string with  spaces  to    remove      ';
cmpthese(-3, {
  'Regexp-Common' => sub { $_=$f; s/$RE{ws}{crop}//g;    },
  'two-s///'      => sub { $_=$f; s/^\s+//; s/\s+$//;    },
  'one-s///'      => sub { $_=$f; s/^\s+|\s+$//g;        },
  's-capture'     => sub { $_=$f; s/^\s*(.*?)\s*$/$1/;   },
  's-capture2'    => sub { $_=$f; s/^\s*(\S+(?:\s+\S+)?)?\s*$/$1/; },
  'm-capture'     => sub { $_=$f; ($_) = /(\S+(?:\s+\S+)?)/;    },
});
[download]

                 Rate Regexp-Common s-capture one-s/// s-capture2 m-ca
+pture two-s///
Regexp-Common   659/s            --      -91%     -93%       -95%     
+ -96%     -97%
s-capture      7002/s          963%        --     -21%       -45%     
+ -59%     -73%
one-s///       8857/s         1244%       26%       --       -30%     
+ -48%     -66%
s-capture2    12699/s         1827%       81%      43%         --     
+ -26%     -51%
m-capture     17179/s         2507%      145%      94%        35%     
+   --     -34%
two-s///      25941/s         3837%      270%     193%       104%     
+  51%       --
[download]

Not surprisingly, the straightforward method of calling s/// twice is the fastest. What is surprising is how slow Regexp-Common turns out to be, and I was pleasantly surprised at how well m-capture did. If, for some bizarre reason, you needed a single atomic expression to remove leading and trailing whitespace, that would seem to be the way to go.

Comment on Re: How do I remove whitespace at the beginning or end of my string? Select or Download Code

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Re: Answer: How do I remove whitespace at the beginning or end of my string? by ysth (Canon) on Jan 27, 2004 at 22:17 UTC
~~Why are you penalizing the one-regex methods by requiring a separate assignment to $_?~~ You should perhaps do 2 separate benchmarks; one assuming $_ is to be changed, and the other assuming a lexical $f is to be changed. Update: I'm just saying that benchmarks for performing an operation on $_ won't necessarily carry over to benchmarks for performing an operation on a lexical. In fact, with a lexical, the two-regex method outshines the others even more: use Benchmark 'cmpthese'; use Regexp::Common 'whitespace'; my $f = ' this is a string with spaces to remove '; cmpthese(-3, { 'Regexp-Common' => sub { my $g=$f; $g=~s/$RE{ws}{crop}//g; }, 'two-s///' => sub { my $g=$f; $g=~s/^\s+//; $g=~s/\s+$//; }, 'one-s///' => sub { my $g=$f; $g=~s/^\s+\|\s+$//g; }, 's-capture' => sub { my $g=$f; $g=~s/^\s(.?)\s$/$1/; }, 's-capture2' => sub { my $g=$f; $g=~s/^\s(\S+(?:\s+\S+)?)?\s*$/$ +1/; }, 'm-capture' => sub { my $g=$f; ($g) = $g=~/(\S+(?:\s+\S+)?)/; + }, }); [download] shows "two-s" gaining more than the others when working on lexicals.	[reply] [d/l]
Re: Re: Answer: How do I remove whitespace at the beginning or end of my string? by Roy Johnson (Monsignor) on Jan 27, 2004 at 23:52 UTC
The test is to remove leading and trailing whitespace from a string. The assignment to $_ is an initialization condition of the test: it has to have the string value in it, and then have the whitespace removed. Update: Oh, now I understand what you're saying. It just didn't occur to me that it could make a significant difference what kind of variable was being operated on. The PerlMonk `tr///` Advocate	[reply]
Correction: How do I remove whitespace at the beginning or end of my string? by Roy Johnson (Monsignor) on Jan 28, 2004 at 18:39 UTC
Argh! The m-capture regex has a bug: the final ? should be a * (and the corresponding ? in s-capture2). Naturally, this slows things down a bit (and I can't update the original answer). Corrected code: `'s-capture2' => sub { $_=$f; s/^\s(\S+(?:\s+\S+))?\s$/$1/; }, 'm-capture' => sub { $_=$f; ($_) = /(\S+(?:\s+\S+))/; },` [download] New results (on a different machine): `Rate Regexp-Common s-capture one-s/// s-capture2 m-c +apture two-s/// Regexp-Common 6629/s -- -89% -90% -91% + -94% -97% s-capture 62950/s 850% -- -1% -18% + -41% -71% one-s/// 63621/s 860% 1% -- -17% + -41% -71% s-capture2 77016/s 1062% 22% 21% -- + -28% -65% m-capture 107187/s 1517% 70% 68% 39% + -- -51% two-s/// 219320/s 3209% 248% 245% 185% + 105% --` [download] The PerlMonk `tr///` Advocate	[reply] [d/l] [select]