neilwatson has asked for the wisdom of the Perl Monks concerning the following question:

Consider this code: 

#!/usr/bin/perl -w

use strict;
use warnings;

my @array = qw(part1
        part2
        part3
        part4
        part5
        part6
        part7
        part8
);

#remove part4
splice @array, 5, 1;

print @array;

[download]

Now consider the output: 

part1part2part3part4part5part7part8

[download]

Should part4 not have been removed from @array? I'm using perl 5.6.1.

Neil Watson
watson-wilson.ca

Replies are listed 'Best First'.
Re: Splice not working or is it me?
by George_Sherston (Vicar) on Sep 14, 2002 at 12:34 UTC 
    #!/usr/bin/perl -w

use strict;
use warnings;

my @array = qw(
        part1
        part2
        part3
        part4
        part5
        part6
        part7
        part8
);

#remove part4 - which is $array[3], not $array[5]!
splice @array, 3, 1;

print @array;

    [download]
    BTW, does anyone else familiar with rope-making and sailing think that splice is exactly the wrong name for this function?

    § George Sherston
[reply]
[d/l]
[select]

      Could it be referring to the 4 argument version of splice and that when you splice a rope to make a fixed loop for instance, you have to squeeze one part of the splitted rope back inbetween the rope itself??

      Just my 2 öre

[reply]
Re: Splice not working or is it me?
by broquaint (Abbot) on Sep 14, 2002 at 12:39 UTC
    That works as expected 
    #              0     1     2     3     4     5     6     7
my @array = qw(part1 part2 part3 part4 part5 part6 part7 part8);
print splice(@array, 5, 1), $/;
print @array;

__output__

part6
part1part2part3part4part5part7part8

    [download]
    As the docs for splice say, it Removes the elements designated by OFFSET and LENGTH from an array, and replaces them with the elements of LIST, if any.
    HTH

    _________
    broquaint

[reply]
[d/l]
Re: Splice not working or is it me?
by kabel (Chaplain) on Sep 14, 2002 at 12:37 UTC
    the output is perfectly right. you counted the wrong direction ;) 
    name    => elem. no
part1   => 0
part2   => 1
part3   => 2
part4   => 3
part5   => 4
part6   => 5
part7   => 6
part8   => 7

    [download]
    splice @array, 5, 1 is translated: get one element from the fifth element on out of the array @array (and replace it with nothing)
[reply]
[d/l]
Re: Splice not working or is it me?
by particle (Vicar) on Sep 14, 2002 at 17:05 UTC
    noone's mentioned it yet, so i'll ask... why are you using -w and use warnings?

    use -w for backward compatibility. require 5.006; use warnings; for new code. don't use both, you'll get into trouble that way. read perllexwarn for more -- specifically What's wrong with -w and $^W.

    ~Particle *accelerates*

[reply]
[d/l]
[select]
Re: Splice not working or is it me?
by neilwatson (Priest) on Sep 14, 2002 at 16:35 UTC
    You are all right. It is me. I've discovered my problem: 

    while ($x <= @array){
   if ($array[$x] =~ m/$regex/){
       splice @array, $x, 1;
   }
}

    [download]

    The problem is that if I remove, for example, element 4 now element 5 becomes element 4 and therefore it is never checked. How can I prevent this?

    Neil Watson
    watson-wilson.ca

[reply]
[d/l]
      Use grep(): @array = grep !/$regex/, @array; Otherwise, with your while loop: 
      $x = 0;
while ($x < @array) {  # NOT <=, but <
  if ($array[$x] =~ /$regex/) { splice @array, $x, 1 }
  else { ++$x }
}

      [download]
      That way you only increment if a match wasn't found.

      _____________________________________________________
      Jeff[japhy]Pinyan: Perl, regex, and perl hacker, who'd like a job (NYC-area)
      s++=END;++y(;-P)}y js++=;shajsj<++y(p-q)}?print:??;

[reply]
[d/l]
[select]
[reply]

Back to Seekers of Perl Wisdom