It appears to me that your datafiles have a hierarchical structure. So you'll have to parse them, and I think, for a generic parsing routine (now you only have to merge the files, but I'm sure that later on you'll have to write a similar script to do other stuff to the same files), it makes the most sense to parse the data into a data structure (a tree); see perldsc and perllol to see what kind of stuff I'm talking about.

Load all datafiles in a proper manner into the same data structure.

As a second step, you'll have to produce the desired output from the produced tree.

Step 1: load the data from all files into a data structure:

my @files = qw(File1.txt File2.txt);
my %tree;
my(@iterations, @names);  # order
foreach my $file (qw(File1.txt File2.txt)) {
    open my $fh, '<', $file or die "Cannot open file $file: $!";
    (my $name = $file) =~ s/\.\w+$//;  # remove extension
    push @refs, $ref;  # order
    my($iteration);
    while(<$fh>) {
        chomp;
        if(/^Iteration /) {
            $iteration = $_;
            push @iterations, $iteration unless $tree{$iteration};  # 
+key order
        } elsif(my($i) = /^(\d+):/) {
            $tree{$iteration}[$i]{$name} = $_;
        }
    }
}
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You can show the contents of the data structure, to see if it works:

use Data::Dumper;
print Dumper \%tree;
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Step 1 is done. Now step 2: print out the data to a file.

foreach my $iteration (@iterations) {
    print "$iteration\n";  # section header
    my $section = $tree{$iteration};  # array ref
    for my $i (0 .. $#$section) {
        my @data;
        foreach my $name (@names) {
            my $data = $section->[$i]{$name};
            next unless defined $data;
            push @data, "$name:$data";
        }
        if(@data) {
            my $line = join " ", @data;
            print "$line\n";
        }
    }
}
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I think that rounds it up...

Similar to the idea given by bart and dwm042 above but a slightly different implementation using a hash of hashes with multiple values per key.

#!/usr/bin/perl -w

use strict;

my @list_of_files =  qw(file1.txt file2.txt);
my %data;
my $file_num = 0;

foreach my $file_name(@list_of_files){
    $file_num++;
    my $file = 'File'.$file_num;
    my $iter;
    my $flag = 0;

    open FH, $file_name or die "Cannot open $file_name. $!";
    while(<FH>){
        chomp;
        if($_ =~ /(Iteration.+)/){
            $iter = $1;
            $flag = 1;
            next;
        }
        if(/^$/){ $flag = 0; }
        if($flag){ push( @{$data{$iter}{$file}}, $_ ); }
    }
    close FH;
}

foreach my $iter ( sort keys %data ) {
    print "$iter\n";
    my $size;
    my $index = 0;
    do {
         for my $file ( sort keys %{ $data{$iter} } ) {
            print "$file: ", @{$data{$iter}{$file}}[$index], " ";
            $size = $#{$data{$iter}{$file}};
        }
        $index++;
        print "\n";
    }
    while($index<=$size);
    print "\n";
}
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#!/usr/bin/perl

use strict;

my $file1 = <<END_FILE2;
Iteration 1:
0: Data: 1023 1023
1: Data: 200 1023
2: Data: 300 1023
3: Data: 250 1023
4: Data: 1023 1023

Iteration 2:
0: Data: 1023 1024
1: Data: 1023 60
2: Data: 1023 90
3: Data: 1023 100
4: Data: 1023 1023
END_FILE2

my (%record, $key);

for my $i (\$file1) {
    open( my $file_1, '<', $i ) or die "cannot open file";
    while( <$file_1> ) {
        $key = $1 if ( s/^(Iteration \d\d?):// );
        push( @{ $record{$key} }, $1 ) if ( /(\d:\s.*)/ );
    }
    close( $file_1 );
}

while (my $line = <DATA>) {
    if ( $line =~ s/^(Iteration \d\d?):// ) {
        $key = $1;
        print "$key:\n";
    }
    my ($index) = $line =~ /^(\d)/;
    print "File1:$record{$key}->[$index] File2:$line" 
      if ( defined( $index ) );
    print "\n" if ( $index == $#{ $record{$key} } );

}

__DATA__
Iteration 1:
0: Data: 1023 1023
1: Data: 250 1023
2: Data: 60 1023
3: Data: 99 1023
4: Data: 1023 1023

Iteration 2:
0: Data: 1023 1024
1: Data: 1023 60
2: Data: 1023 90
3: Data: 1023 100
4: Data: 1023 1023
[download]

Thanks to all Perl monks (bart,arun,bichonfrise74) for providing the solutions. Really helped in learning the perl concepts

Hello Monks, I could merge the input files in row wise, i am not able to merge it in column wise, as expected, Please help.

Below code i wrote which will merge row wise

lnin,

bart above really does have the answer to this question. You can't easily read data and then immediately write data any way you please. To write the data column-wise or anyway-wise, it's best to:


• read all the data and store it.
• write the data out in the format you want.
Given that you are wanting to write out the data in terms of iterations and line numbers, the data can be stored in an array (as pairs of numbers, for example). The index to the array can be the number of the iteration.