Re: How to remove character at certain position in the String.....

I'd probably do it with substr, usually, but you can do it using a regexp too. As the regexp does not match if you do not have enough chars, you do not have to worry about malformed strings (you only 'touch' strings that are meaningful).

This is a sample:

use strict;
my $a;
my $from = 2;
my $len  = 2;

while( $a = <DATA> ) {
    chomp $a;
    print "Before: '$a' ";
    $a = $1 . $2 if $a =~ /^(.{$from}).{$len}(.*)$/i;
    print "After '$a'\n";
}

__DATA__
12345678
yellow
a
xx
yyy
[download]

Comment on Re: How to remove character at certain position in the String..... Download Code

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Re: Re: How to remove character at certain position in the String..... by jweed (Chaplain) on Dec 02, 2003 at 09:43 UTC
I would use `qr//` to compile the regex before the loop so you don't have the (potentially) large overhead each iteration. Update I am wrong. Do not listen to me. Who is Kayser Söze?	[reply] [d/l]
Re: How to remove character at certain position in the String..... by Abigail-II (Bishop) on Dec 02, 2003 at 10:19 UTC
What potential overhead? Perl will not recompile the regex in each iteration (unless you modify $from or $len). Here's a proof, assuming the program is in the file `/tmp/qq`: $ perl -Dr /tmp/qq 2>&1 \| grep Compiling Compiling REx `^(.{2}).{2}(.)$' $ [download] It only gets compiled once. Here's a benchmark: #!/usr/bin/perl use strict; use warnings; use Benchmark 'cmpthese'; our @data = <DATA>; chomp @data; our $from = 2; our $len = 2; our (@a, @b, @c); cmpthese -10 => { substr => 'for (@a = @data) { substr $_, $from, $len, "" if length ($_) >= $fro +m + $len }', regex => 'for (@b = @data) { $_ = $1 . $2 if /^(.{$from}).{$len}(.)$/; }', regex_qr => 'my $qr = qr /^(.{$from}).{$len}(.*)$/; for (@c = @data) { $_ = $1 . $2 if /$qr/; }', }; die "Unequal" unless "@a" eq "@b" && "@b" eq "@c"; __DATA__ 12345678 yellow a xx yyy a somewhat longer line to compensate for the smaller lines. bla bla bla bla Rate regex_qr regex substr regex_qr 38207/s -- -3% -62% regex 39497/s 3% -- -60% substr 99555/s 161% 152% -- [download] Abigail	[reply] [d/l] [select]
/$variable/ [was: Re: Re: How to remove character at certain position in the String.....] by bronto (Priest) on Dec 02, 2003 at 10:47 UTC
Interesting! Like jweed, I knew that if you use `/$variable/` in a cycle, it gets recompiled at each iteration, even if `$variable` doesn't change. Since I am sure I read that in a far away day in the past `;-)` I suppose that it worked that way before, so it must have changed at some point. Could anybody tell at which version of Perl that behaviour changed? Thanks Ciao! `--bronto` The very nature of Perl to be like natural language--inconsistant and full of dwim and special cases--makes it impossible to know it all without simply memorizing the documentation (which is not complete or totally correct anyway). --John M. Dlugosz	[reply] [d/l] [select]


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