Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl-Sensitive Sunglasses
 
PerlMonks  

Re^2: finding number of contiguous letters

by GrandFather (Sage)
on May 23, 2007 at 08:11 UTC ( #616951=note: print w/replies, xml ) Need Help??


in reply to Re: finding number of contiguous letters
in thread finding number of contiguous letters

Right you are ;)

use warnings; use strict; use Benchmark qw(cmpthese); my $str = "Just Another Perl Hacker"; print join " ", do_substr (), "\n"; print join " ", do_regex (), "\n"; print join " ", do_unpack (), "\n"; print "\n"; cmpthese (-1, { unpack => \&do_unpack, substr => \&do_substr, regex => \&do_regex, } ); sub do_substr { my @parts; push @parts, substr $str, $_, 3 for 0 .. length ($str) - 3; return @parts; } sub do_regex { my @parts = $str =~ /(?=(...))/g; return @parts; } sub do_unpack { my $matches = length ($str) - 2; my $temp = "a3XX" x $matches; my @parts = unpack ($temp, $str); return @parts; }

Prints:

Jus ust st t A An Ano not oth the her er r P Pe Per erl rl l H H +a Hac ack cke ker Jus ust st t A An Ano not oth the her er r P Pe Per erl rl l H H +a Hac ack cke ker Jus ust st t A An Ano not oth the her er r P Pe Per erl rl l H H +a Hac ack cke ker Rate regex unpack substr regex 42045/s -- -12% -39% unpack 47764/s 14% -- -31% substr 69161/s 64% 45% --

Update: added unpack


DWIM is Perl's answer to Gödel

Replies are listed 'Best First'.
Re^3: finding number of contiguous letters
by Skeeve (Parson) on May 23, 2007 at 12:31 UTC

    I beg to differ...

    For this substr based implementation it's important to have the temporary array @parts. For the regex it's unimportant! So if we leave the assignment to the array out, the regex is way faster!

    Update: Can this be due to the fact that the functions might be called in a scalar context?

    use warnings; use strict; use Benchmark qw(cmpthese); my $str = "Just Another Perl Hacker"; print join " ", do_mapstr (), "\n"; print join " ", do_substr (), "\n"; print join " ", do_regex (), "\n"; print "\n"; cmpthese (-1, { mapstr => \&do_mapstr, substr => \&do_substr, regex => \&do_regex, } ); sub do_mapstr { return map substr($str,$_-3,3),(3..length $str); } sub do_substr { my @parts; push @parts, substr $str, $_, 3 for 0 .. length ($str) - 3; return @parts; } sub do_regex { return $str =~ /(?=(...))/g; }

    Result

    Jus ust st t A An Ano not oth the her er r P Pe Per erl rl l H H +a Hac ack cke ker Jus ust st t A An Ano not oth the her er r P Pe Per erl rl l H H +a Hac ack cke ker Jus ust st t A An Ano not oth the her er r P Pe Per erl rl l H H +a Hac ack cke ker Rate substr mapstr regex substr 25123/s -- -48% -97% mapstr 48651/s 94% -- -95% regex 1003705/s 3895% 1963% --

    s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
    +.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e
Re^3: finding number of contiguous letters
by Limbic~Region (Chancellor) on May 23, 2007 at 12:44 UTC
    GrandFather,
    If you are feeling bored, I would be interested in seeing how my unpack solution I came up with for Challenge: Fast Common Substrings does. In a nutshell, we programmatically generate a template to extract all substrings of a given length.

    Cheers - L~R

      More interested than bored. Note that removing the template generation from do_update makes no significant difference to the result.


      DWIM is Perl's answer to Gödel
        GrandFather,
        Neat and thanks. I am interested myself but am finding myself with no free time. The next question I would want to ask is if the results change as the size of string changes. Oh well, another time perhaps. Thanks again.

        Cheers - L~R

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://616951]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others exploiting the Monastery: (4)
As of 2020-10-27 20:03 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    My favourite web site is:












    Results (257 votes). Check out past polls.

    Notices?