array element question

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

I'm trying to find a way to concatentate subsequent array elements into a new array upon matching a string walking an array. For example:

#!/usr/bin/perl
my $file = '/output.txt';
open DATA, "$file" or die "can't open file";
my @array = <DATA>;
  for($i=1; $i < 10; $i++) {
    foreach my $found ($array[$i]) {
      if ( $found =~ /string1/ ) {
        my @new = join($array[$i], $array[$i++]);
      }
    }
  }
close (DATA);
[download]

Let's say "string1" is $array[2] now I want to be able to create a @new with $array[2] and $array[3] concatentated. I'm guessing I'd use join somehow (ie, my @new = join($array[$i], $array[$i+1];), but am having problems figuring out how to do $array[$?] + 1 element when I don't know statically what the matching array element number is.

Anybody have any idea's?

Thanks,

Jim

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Re: array element question by jdporter (Paladin) on Nov 21, 2006 at 23:16 UTC
In situations like this, I find it a little more natural to shift off the elements, rather than iterate using a counter. But it means you have to take measures to keep from destroying the source, if that would matter. Putting it all in a subroutine can provide this measure of safety. `sub foo # not sure what you'd call this { my $pat = shift; my @r; while (@_) { my $x = shift; push @r, $x; $x =~ /$pat/ and $r[-1] .= shift; } @r } my @new = foo( qr/string1/, @array );` [download] We're building the house of the future together.	[reply] [d/l]
Re: array element question by chromatic (Archbishop) on Nov 22, 2006 at 02:13 UTC
`my @new = join($array[$i], $array[$i++]);` Be very careful with that. Who knows when the `++` will happen in relation to the array accesses! (I think you can guarantee that it will happen before the second one, but how about in relation to the other?	[reply] [d/l] [select]
Re^2: array element question by robot_tourist (Hermit) on Nov 22, 2006 at 14:26 UTC
probably best not to use assignments in array access. You'll need another line of code to do the increment, but I think it's worth it. How can you feel when you're made of steel? I am made of steel. I am the Robot Tourist. Robot Tourist, by Ten Benson	[reply]
Re: array element question ($prev) by tye (Sage) on Nov 21, 2006 at 23:53 UTC
`my @new; my $prev= ''; my $found= 0; while( <DATA> ) { if( $found ) { push @new, $prev . $_; } $found= /string1/; $prev= $_; }` [download] - tye	[reply] [d/l]
Re^2: array element question ($prev) by Anonymous Monk on Nov 22, 2006 at 00:45 UTC
Thanks for all the responses!!	[reply]
Re: array element question by GrandFather (Saint) on Nov 21, 2006 at 23:24 UTC
If you don't mind clobbering the array or copying it to a temporay version then you can: `use strict; use warnings; my @array = <DATA>; chomp @array; for my $index (0 .. $#array) { next unless $array[$index] =~ /'/ && exists $array[$index + 1]; $array[$index] .= $array[$index + 1]; $array[$index + 1] = ''; } @array = grep {length} @array; print join "\n", @array; __DATA__ I' m guessing I' d use join somehow` [download] Prints: `I'm guessing I'd use join somehow` [download] DWIM is Perl's answer to Gödel	[reply] [d/l] [select]