Hello,
sorry for the much delayed reply, and thanks for the information.

I've come across this node while searching for something else.

I've used Tie::IxHash and it has worked.Here is the code:

use Tie::IxHash;

open DF, 'd.txt' or die $!;
my %tagdict;  
while (<DF>) {  
chomp;  
my ($word, $cat) = split;
$tagdict{$word} = $cat; 
}

while ( ($k,$v) = each %tagdict ) {
#print "$k => $v\n";
}

close DF;

open CF, 'c.txt' or die $!;
my %tagcorpus; 

tie %tagcorpus,"Tie::IxHash";

while (<CF>) {  
chomp;  

my @cwords = split; 
@tagcorpus{@cwords} = (1) x @cwords;   
}

while ( ($k,$v) = each %tagcorpus ) {
#print "$k => $v\n";
}

close CF;


open CF, '+<c.txt' or die $!;

seek CF, 0, 0; # go to start of file 
   truncate CF, 0; 
       
       foreach $citem(keys %tagcorpus){
               #print "\n$citem";
                          
           print CF $citem;
               print CF " ";
                            
           foreach $ditem(keys %tagdict){
                 my $currentposition=tell CF;
                 seek CF,0,1 ;
                 
                 if ($citem eq $ditem){
                    print CF "$tagdict{$ditem}";
                 }
              }      
           }  
                               
   close CF;
[download]

Cheers.