Perl Guru Forums: Perl Programming Help: Regular Expressions: Corrected - Please read again: Regexp to remove a matched pattern but...

CGI/Perl Guide | Learning Center | Forums | Advertise | Login

Site Search: in


	MAIN INDEX	SEARCH POSTS	WHO'S ONLINE	LOG IN

Home: Perl Programming Help: Regular Expressions:
Corrected - Please read again: Regexp to remove a matched pattern but...

Chupo_cro
Novice

Aug 25, 2012, 5:19 AM

Post #1 of 10 (7275 views)

Corrected - Please read again: Regexp to remove a matched pattern but...	Can't Post

Can someone, please, help me to construct the regexp to remove the matched pattern from the string, but to avoid more than one space in the resulting string at the boundaries of the removed substring. All of the remaining substring should stay untouched.

Note: The blue text is a condition I forgot to insert in the inital text.

Example:

Code

Input: 
 
one two some_pattern three four 
one two    some_pattern     three four 
one twosome_pattern     three four 
one two    some_patternthree four 
one two three four some_pattern 
some_pattern  one two three four 
onetwosome_patternthreefour 
one   two some_pattern three       four 
 
Desired output: 
 
one two three four 
one two three four 
one two three four 
one two three four 
one two three four 
one two three four 
onetwothreefour 
one    two three       four

Just removing the

Code

some_pattern

from the

Code

one two some_pattern three four

would result in the string

Code

one two  three four

which has two consecutive spaces.
Chupo_cro

(This post was edited by Chupo_cro on Aug 25, 2012, 9:34 AM)

Laurent_R
Veteran / Moderator

Aug 25, 2012, 7:57 AM

Post #2 of 10 (7268 views)

Re: [Chupo_cro] Regexp to remove a matched pattern but... [In reply to]	Can't Post

Hi,

a suggestion:

Code

$line =~ s/some_pattern//g; # removing the pattern 
$line =~s/(\s)\s+/$1/g; # changing multi space into one space

Chupo_cro
Novice

Aug 25, 2012, 8:50 AM

Post #3 of 10 (7265 views)

Re: [Laurent_R] Regexp to remove a matched pattern but... [In reply to]	Can't Post

In Reply To

Hi,

a suggestion:

Code

$line =~ s/some_pattern//g; # removing the pattern 
$line =~s/(\s)\s+/$1/g; # changing multi space into one space

Yes, that could be a soution. However, I wouldn't want to 'touch' the unmatched part of the string. I am sorry my explanation wasn't precise in that detail. Here you are an additional example to demonstrate the desired output:

Code

Input:  
  
one   two some_pattern three       four 
 
Desired output:  
  
one    two three       four

That is - all of the remaining (unmatched) substring should stay as it was.

Thank you for the reply and sorry for the inconvenience.
Chupo_cro

Laurent_R
Veteran / Moderator

Aug 25, 2012, 11:41 AM

Post #4 of 10 (7253 views)

Re: [Chupo_cro] Regexp to remove a matched pattern but... [In reply to]	Can't Post

Hi,

then you can just replace {one or more spaces, some_pattern, one or more spaces} by one space. Something like this:

Code

$line =~ s/\s+some_pattern\s+/ /g;

Laurent_R
Veteran / Moderator

Aug 25, 2012, 11:45 AM

Post #5 of 10 (7252 views)

Re: [Laurent_R] Regexp to remove a matched pattern but... [In reply to]	Can't Post

Well, looking again at your examples, I figured out that sometimes you do not have a space before or after some_pattern.

It should be rather like this:

Code

$line =~ s/\s*some_pattern\s*/ /g;

Chupo_cro
Novice

Aug 26, 2012, 5:28 PM

Post #6 of 10 (7216 views)

Re: [Laurent_R] Regexp to remove a matched pattern but... [In reply to]	Can't Post

In Reply To

Well, looking again at your examples, I figured out that sometimes you do not have a space before or after some_pattern.

It should be rather like this:

Code

$line =~ s/\s*some_pattern\s*/ /g;

Can you, please, check if this would result in the desired output according to the input/output (one before the last blue example in my first post)? That is:

Code

Input: 
 
onetwosome_patternthreefour 
 
Output: 
 
onetwothreefour

The regexp you wrote seems to handle every case except the case when there isn't a space before or after the pattern.

In words: If there isn't any spaces before or after the pattern, then resulting string after removing the pattern also shouldn't contain the space at the place of the removed string.

I am sorry, just my explanation in words wasn't in-depth enough to completely define the problem - the input/output examples better illustrate what I would like to achieve.

Thank you for your time!
Best Regards,
Chupo_cro

Laurent_R
Veteran / Moderator

Aug 26, 2012, 11:38 PM

Post #7 of 10 (7212 views)

Re: [Chupo_cro] Regexp to remove a matched pattern but... [In reply to]	Can't Post

Then you probably need several regexes to handle the differents cases, something like this

$line =~ s/\s+some_pattern[^\s]/ /g;
$line =~ s/[^\s]some_pattern\s+/ /g;
$line =~ s/\s+some_pattern\s+/ /g;
$line =~ s/some_pattern//g;

Chupo_cro
Novice

Aug 28, 2012, 2:56 AM

Post #8 of 10 (7202 views)

Re: [Laurent_R] Regexp to remove a matched pattern but... [In reply to]	Can't Post

In Reply To

I still haven't done the testing but am pretty sure it is going to handle all of the inputs (space(s)+not-space, not-space+space(s), space(s)+space(s), no spaces).

Thank you very much for your time! I appreciate your help,

Best Regards
Chupo_cro

Laurent_R
Veteran / Moderator

Aug 28, 2012, 4:44 AM

Post #9 of 10 (7193 views)

Re: [Chupo_cro] Regexp to remove a matched pattern but... [In reply to]	Can't Post

Yes, do the testing. I haven't tested it at all, and this was just a quick answer from the top of my mind.

BillKSmith
Veteran

Aug 28, 2012, 6:04 AM

Post #10 of 10 (7184 views)

Re: [Chupo_cro] Regexp to remove a matched pattern but... [In reply to]	Can't Post

I am sure that Laurent is on the right track. This will take more than one Regex. I recommend that you implement the solution as a subroutine. For testing purposes, it may worth the extra effort to package that subroutine as a module.

The subroutine should be tested with one of perl's test modules. http://search.cpan.org/~rgarcia/perl-5.10.0/lib/Test/Tutorial.pod. Your specification is already in exactly the form that you need.

EDITS: I have replaced the code in this post. The failures reported by the original were correct. I have improved the output of the test and replaced the regular expressions with a new set. The new subroutine now passes all but the blue test case. The test case appears to have too many spaces between 'one' and 'two'. I have taken the liberty of changing that in my test. The code now posted below passes all tests (including the extra one I describe below)

Code

use strict; 
use warnings; 
use Test::More qw( no_plan ); 
 
my %fixed_line = ( 
    'one two some_pattern three four'         => 'one two three four', 
    'one two    some_pattern     three four'  => 'one two three four', 
    'one twosome_pattern     three four'      => 'one two three four', 
    'one two    some_patternthree four'       => 'one two three four', 
    'one two three four some_pattern'         => 'one two three four', 
    "one two three four some_pattern\n"         => "one two three four\n", 
    'some_pattern  one two three four'        => 'one two three four', 
    'onetwosome_patternthreefour'             => 'onetwothreefour', 
    'one   two some_pattern three       four' => 'one   two three       four', 
); 
 
foreach my $line (keys %fixed_line) { 
    my $expected = $fixed_line{$line}; 
    my $computed = fix($line); 
    is( $computed, $expected, "'$line' => '$computed'" ); 
} 
 
sub fix { 
    my ($line) = @_; 
    $line =~ s/(?:^\s*some_pattern\s*)|(?:\s*some_pattern$)//; 
    $line =~ s/(?<=\S)some_pattern(?=\S)//; 
    $line =~ s/\s*some_pattern\s*/ /; 
    return $line; 
}

There are other issues which should be tested. Regexps treat Tabs and Newlines as whitespace. That may not be what you want. (e.g. your fifth case would be much different there were a newline at the end.)

I suspect that you will continue to discover special cases for some time. This kind of test will assure you that proposed fixes do not break the old code.
Good Luck,
Bill

(This post was edited by BillKSmith on Aug 28, 2012, 9:25 AM)

Search for (options)

Web Applications & Managed Hosting Powered by Gossamer Threads
Visit our Mailing List Archives