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

How do you write the characters in certain array of the first file in reverse order merging with the array on a second file in a reverse order too. For example, File 1 contains: abcde; and File2 contains: ijklm .I want to write: me ld kc jb ia. Thankx perl masters!

Replies are listed 'Best First'.
Re: Writing in reverse
by chromatic (Archbishop) on Aug 01, 2000 at 04:22 UTC
    Untested code follows. It's highly inefficient, but you get the idea: 
    my (@first, @second);

{

    local *FILE1;

    local *FILE2;

    open(FILE1, $file1) || die "Can't open $file1: $!";

    open(FILE2, $file2) || die "Can't open $file2: $!";

    @first = reverse split(//, <FILE1>);

    @second = reverse split(//, <FILE2>);

    close FILE1;

    close FILE2;

}



while (@first) {

    my $couplet = shift @first . shift @second;

    print "$couplet ";

}

    [download]
    A more efficient technique would involve substr and not that yucky reverse split magic, which may not work anyway. (I'm not at a machine where I can test this right now.)

    Update: chop is a better solution yet.

[reply]
[d/l]
      @first = reverse split //, <FILE1>;

      [download]
      will only operate on the first line of the file because split forces the filehandle into a scalar context.
[reply]
[d/l]
Re: Writing in reverse
by eak (Monk) on Aug 01, 2000 at 06:42 UTC
    Here is another way to do it using chop. 
    #!/usr/bin/perl -w
use IO::File;
 
 
my $fh1 = new IO::File;
my $fh2 = new IO::File;
 
$fh1->open("< file1.txt") or die "can't open file1.txt $!";
$fh2->open("< file2.txt") or die "can't open file2.txt $!";
 
 
my $file1 = <$fh1>;
my $file2 = <$fh2>;
 
print "Merging:\n";
print "\t$file1\n";
print "\t$file2\n";
 
while(length $file1){
  my $couplet = chop($file1).chop($file2);
  print "$couplet ";
}

    [download]
[reply]
[d/l]
      Eak, Thankx for the answer, What if I want the arrays to merge in backward order? like first file is : abcde, second file is fghij, I want ej di ch bg af. By the way it only worked for one array only rather than whole file . It didn't read whole file for some reason. Thankx.
[reply]
        never mind..I got it
[reply]
      You fell into the same trap as chromatic in that you only read the first line of the file. Either localize $/ to undef or use my @file1 = <$fh1>

      Other then that though, this is very slick and you use a much better way of scoping the file handle.

[reply]
RE: Writing in reverse
by larsen (Parson) on Aug 01, 2000 at 14:01 UTC
    What about this solution? # Two string of the SAME length? my $length; open( FILE1, "string1" ); open( FILE2, "string2" ); $string1 = <FILE1>; $string2 = <FILE2>; map { $a = substr($string1, $_, 1); $b = substr($string2, $_, 1); print "$b$a "; } reverse(0 .. length($string1) - 1);
[reply]

      If you edit your node and put <CODE> ... </CODE> tags around the code then it will be far more legible and your <FILE1> and <FILE> expressions won't be interpeted as HTML tags.

      At the same time, you should probably consider checking the return value from the open function. I realise that this is just an example, but people will copy and paste it, so you should make it as safe as possible.

      --
      <http://www.dave.org.uk>

      European Perl Conference - Sept 22/24 2000, ICA, London
      <http://www.yapc.org/Europe/>
[reply]
        I see your point. Thank you :)
[reply]
      Excuse me for my badly formatted reply.
I've missed to RTF.How To display...:>

Here the piece of code I suggest:

my $length;

open( FILE1, "string1" );
open( FILE2, "string2" );

$string1 = <FILE1>;
$string2 = <FILE2>;

map {
	$a = substr($string1, $_, 1);
	$b = substr($string2, $_, 1);
	print "$b$a ";
} reverse(0 .. length($string1) - 1);
[reply]

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