use strict;
use warnings;

my( %file, $idx, %cat,$x);
$idx=1;                          # Start at 1 to avoid using the //= operator  
while (<>){                      # read all files in @ARGV
  chomp;
  my ($c,$val)=split;            # Separate the category from the value
  next unless $c;                # Skip blank lines       
  $file{$ARGV} ||= $idx++;       # Increment $idx for each new file
  $cat{$c}[ $file{$ARGV} ] = $val; # Save in $cat{Category}[FileIdx]
}

print "\t",map ({"$_\t"} sort keys %file),"\n"; # List of files

my @FileIndexes = map {$file{$_}}  sort keys %file;
for my $k (sort keys %cat){
  print "$k\t",map({(defined($x=$cat{$k}[$_])?$x:"")."\t"} 
             @FileIndexes),"\n";


}