This one works with a list of simple files: 
use strict;
use warnings;

my( %file, $idx, %cat,$x);
$idx=1;                          # Start at 1 to avoid using the //= o
+perator  
while (<>){                      # read all files in @ARGV
  chomp;
  my ($c,$val)=split;            # Separate the category from the valu
+e
  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";


}

[download]
Run and results: 
$ perl  test-tab1.pl test-tabd*
    test-tabdata.txt    test-tabdata2.txt    test-tabdata2.txt~    
A    12    33    9    
B    152    221    333    
C    123    423    444    
D    456    43    555    
E        99

[download]
update:Noticed you were "new to perl", so I added comments, and simplified a bit
update2:Fixed subtle bug in first value not being reported as noted by sauoq below (FWIW,I found it independently)

             I hope life isn't a big joke, because I don't get it.
                   -SNL

In reply to Re: simple table join script by NetWallah
in thread simple table join script by slavailn

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