Re^2: Seeking Audience with the Perl Regex Droids...

Your solution is actually incorrect on parsing any string which has a consecutive stretch of pound signs (ie '#') that is a multiple of 4 and greater than or equal to 8.

Try this:

my $x = '@########@';
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it should parse as:

    '',
    '####',
    '',
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Your solution (as you've hard coded it for one example, and admittedly so in your post), returns:

   '',
   '###@'
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which would have been delimited as:

'@#######@'
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That is, seven pound signs...

I ask you to please consider the original post as I dont think you are making your assertions with an understanding of what was asked. For example, the escape character itself must be escaped when created a delimited line. Hence the list:

my @x = qw(## @ #);
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would be delimited as:

'####@#@@##'
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Finally, I would be glad to verify your second claim if you can provide the input string upon which rollahead and unroll return different results. I believe such a string does not exist.

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Re^3: Seeking Audience with the Perl Regex Droids... by BrowserUk (Patriarch) on Mar 29, 2008 at 09:04 UTC
Finally, I would be glad to verify your second claim if you can provide the input string upon which rollahead and unroll return different results. I believe such a string does not exist. Actually, it was your own benchmark: #! perl -slw use strict; use Benchmark ':all', ':hireswallclock'; my $x = "#@##@###@####@#####@"; my $y = reverse $x; my $z = "$x$x$x$y$y$x$x$y$y$y$y$y$x$x$x$x"; our %results; cmpthese -3, { unroll => sub { my @x = ([unroll($x)],[unroll($y)],[unroll($z)]); $results{ unroll } = \@x; }, rollahead => sub { my @x = ([rollahead($x)],[rollahead($y)],[rollahead($z)]); $results{ rollahead } = \@x; }, lookbehind => sub { my @x = ([lookbehind($x)],[lookbehind($y)],[lookbehind($z)]); $results{ lookbehind } = \@x; }, }; printf "%20s => %s\n", $_, "@{[ map{ qq[@$_] } @{ $results{ $_ } } ]} +" for keys %results; sub unroll { my @x = $_[0] =~ /(?:^\|@)((?:##\|#@\|[^#@]))/g; for(@x){ $_ =~ s/##/#/g; $_ =~ s/#@/@/g; } @x } sub rollahead { my $x = shift; $x = reverse $x; my @x = reverse(split/\@(?=(?:##)(?!#))/,$x,-1); for(@x){ $_ = reverse; $_ =~ s/##/#/g; $_ =~ s/#@/@/g; } @x } sub lookbehind { my $x = shift; split m[ (?: (?<=[^#]\#\#\#\#) \| (?<=[^#]\#\#) \| (?<!\#) ) [@] ]x, + $x; } [download] Output (read'em and weep:): C:\test>junk8 Rate unroll rollahead lookbehind unroll 3096/s -- -3% -33% rollahead 3175/s 3% -- -32% lookbehind 4639/s 50% 46% -- rollahead => @# #@## ##@ ##@## #@# # @# #@## ##@@# #@## ## +@@# #@## ##@ ##@## #@# @##@## #@# # # #@## ##@@# #@## ##@ ##@## #@# @ +##@## #@# @##@## #@# @##@## #@# @##@## #@# # # #@## ##@@# #@## ##@@# +#@## ##@@# #@## ##@ unroll => @# #@## ##@ ##@## #@# @# #@## ##@@# #@## ##@ +@# #@## ##@ ##@## #@# @##@## #@# # # #@## ##@@# #@## ##@ ##@## #@# @# +#@## #@# @##@## #@# @##@## #@# @##@## #@# # # #@## ##@@# #@## ##@@# # +@## ##@@# #@## ##@ lookbehind => #@## ###@#### #####@ #####@#### ###@## # #@## + ###@#### #####@#@## ###@#### #####@#@## ###@#### #####@ #####@#### # +##@## #@#####@#### ###@## ## ## ###@#### #####@#@## ###@#### #####@ # +####@#### ###@## #@#####@#### ###@## #@#####@#### ###@## #@#####@#### + ###@## #@#####@#### ###@## ## ## ###@#### #####@#@## ###@#### #####@ +#@## ###@#### #####@#@## ###@#### #####@ [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l] [select]

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Re^3: Seeking Audience with the Perl Regex Droids...
by BrowserUk (Patriarch) on Mar 29, 2008 at 09:04 UTC

Finally, I would be glad to verify your second claim if you can provide the input string upon which rollahead and unroll return different results. I believe such a string does not exist.

Actually, it was your own benchmark:

#! perl -slw
use strict;
use Benchmark ':all', ':hireswallclock';

my $x = "#@##@###@####@#####@";
my $y = reverse $x;
my $z = "$x$x$x$y$y$x$x$y$y$y$y$y$x$x$x$x";

our %results;
cmpthese -3, {
    unroll    => sub {
       my @x = ([unroll($x)],[unroll($y)],[unroll($z)]);
       $results{ unroll } = \@x;
    },
    rollahead => sub {
       my @x = ([rollahead($x)],[rollahead($y)],[rollahead($z)]);
       $results{ rollahead } = \@x;
    },
    lookbehind => sub {
       my @x = ([lookbehind($x)],[lookbehind($y)],[lookbehind($z)]);
       $results{ lookbehind } = \@x;
    },
};

printf "%20s => %s\n", $_,  "@{[ map{ qq[@$_] } @{ $results{ $_ } } ]}
+" for keys %results;

sub unroll {
    my @x = $_[0] =~ /(?:^|@)((?:##|#@|[^#@])*)/g;
    for(@x){
        $_ =~ s/##/#/g;
        $_ =~ s/#@/@/g;
    } @x
}

sub rollahead {
    my $x = shift;
    $x = reverse $x;
    my @x = reverse(split/\@(?=(?:##)*(?!#))/,$x,-1);
    for(@x){
        $_ = reverse;
        $_ =~ s/##/#/g;
        $_ =~ s/#@/@/g;
    } @x
}

sub lookbehind {
    my $x = shift;
    split m[ (?: (?<=[^#]\#\#\#\#) | (?<=[^#]\#\#) | (?<!\#) ) [@] ]x,
+ $x;
}
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Output (read'em and weep:):

C:\test>junk8
             Rate     unroll  rollahead lookbehind
unroll     3096/s         --        -3%       -33%
rollahead  3175/s         3%         --       -32%
lookbehind 4639/s        50%        46%         --
           rollahead => @# #@## ##@  ##@## #@# # @# #@## ##@@# #@## ##
+@@# #@## ##@ ##@## #@# @##@## #@# # # #@## ##@@# #@## ##@ ##@## #@# @
+##@## #@# @##@## #@# @##@## #@# @##@## #@# # # #@## ##@@# #@## ##@@# 
+#@## ##@@# #@## ##@

              unroll => @# #@## ##@  ##@## #@#  @# #@## ##@@# #@## ##@
+@# #@## ##@ ##@## #@# @##@## #@# # # #@## ##@@# #@## ##@ ##@## #@# @#
+#@## #@# @##@## #@# @##@## #@# @##@## #@# # # #@## ##@@# #@## ##@@# #
+@## ##@@# #@## ##@

          lookbehind => #@## ###@#### #####@  #####@#### ###@## # #@##
+ ###@#### #####@#@## ###@#### #####@#@## ###@#### #####@ #####@#### #
+##@## #@#####@#### ###@## ## ## ###@#### #####@#@## ###@#### #####@ #
+####@#### ###@## #@#####@#### ###@## #@#####@#### ###@## #@#####@####
+ ###@## #@#####@#### ###@## ## ## ###@#### #####@#@## ###@#### #####@
+#@## ###@#### #####@#@## ###@#### #####@
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Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

[reply]
[d/l]
[select]