use strict;
use warnings;
# merger v1.2.1
open my $B, '<', 'file_B.txt' or die "Cannot open file_B: $!";
my %functions;
my $i =0;
while (my $line = <$B>) {
    chomp $line;
    $line =~ s/(\d+)\s//;
    $functions{$1} = $line;
}
close $B;

open my $A, '<', 'file_A.txt' or die "Cannot open File_A: $!";
open my $C, '>', 'File_C.txt' or die "Cannot open File_C; $!";
my $prev_id;
while (my $line = <$A>){
    my ($id,$code) = split /\s+/, $line;
    if (!defined $prev_id or $id ne $prev_id){
        print {$C} "\n" if defined $prev_id;
        print {$C} "$id";
        $prev_id = $id;
    }
    else {
        print {$C} ","
    }

    print {$C} "\t$functions{$code}";
}
print {$C} "\n";
close $C;
close $A;
exit 0;