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Split on every second character

by gri6507 (Deacon)
on Feb 12, 2010 at 22:56 UTC ( #822947=perlquestion: print w/ replies, xml ) Need Help??
gri6507 has asked for the wisdom of the Perl Monks concerning the following question:

I have what I thought would be a very simple problem. However, it has me baffled. I have data of the form
"010203040506"
which I would like to split into the form of
"01 02 03 04 05 06"
. The code that I wrote

use strict; use warnings; use Data::Dumper; my @list = split(/(..)/, '010203040506'); print Dumper(\@list); print join(' ', @list)

does the job, but produces empty elements in the list, which results in the undesired output of
" 00  01  02  03  04  05  06"
which contains unwanted spaces. I understand why this is: when splitting on any two characters, the first two are a match, thus, thus they represent the split string (which is element 1), which separates a NULL string (captured in element 0) from the remaining characters (captured in remaining characters). However, I don't want to see the extra spaces in the resulting output. How can I get rid of that?

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Re: Split on every second character
by linuxer (Deacon) on Feb 12, 2010 at 23:00 UTC

    If you are sure that the string is even sized, you can use a simple regex like this:

    use strict; use warnings; my $string = "0102030405"; # will miss the last character when string is odd sized my @elements = $string =~ m/(..)/g; print "@elements\n";
    Update: modified code

      and if you are unsure but want the last character for odd length strings you can:

      my @list = $str =~ /(..?)/g;

      True laziness is hard work
      I didn't think of using the match operator for this. Thanks!
Re: Split on every second character
by ikegami (Pope) on Feb 12, 2010 at 23:06 UTC

    When you use split, the pattern must match what separates what you want. In this case, the separator is the empty string between a character at an odd positions and a character at an even position. That's not exactly straightforward to match, but it's possible.

    $ perl -E'say for split /(?!^|\z)(?(?{ pos()%2 })(?!))/, "0102030405"' 01 02 03 04 05 06

    Here, it's simpler just to match what you want grab rather than what separates them, so just use a m//g:

    $ perl -E'say for "0102030405" =~ /(..?)/sg' 01 02 03 04 05 06
      No wonder getting the split() operator to work correctly was difficult. Thank you!
Re: Split on every second character
by BrowserUk (Pope) on Feb 12, 2010 at 23:21 UTC

    For anything that doesn't require conditional matching, I prefer unpack:

    print for unpack '(A2)*', '010203040506';; 01 02 03 04 05 06

    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.
Re: Split on every second character
by rubasov (Friar) on Feb 13, 2010 at 10:35 UTC
    Or still using split, you can just drop every second element from the result list:
    $ perl -le '@l = grep {$i++ % 2} split /(..)/, "010203040506"; print j +oin "|", @l'
    But the solutions provided by other monks are definitely nicer.

      I agree that some variation of an approach using  m/..?/g or  unpack() is better, but a more concise  split() solution would be:

      >perl -wMstrict -le "print for grep length, split /(..)/, '0001020304101112';" 00 01 02 03 04 10 11 12

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