for my $nr (1..2) {
 for my $line (read_file('file'.$nr)) {
  my @cols = split(/\t/,$line);
  push @{$data[$nr - 1]->{shift(@cols)}},\@cols;
 }
}

##</code><code>##

# expecting file3 line in @col
my @results = ($col[0],$col[3]);
for my $dataset (@data) {
 push @results,(sort {
   my $diff_a = $col[2] - $a->[1];
   $diff_a *= -1 if $diff_a < 0;
   my $diff_b = $col[2] - $b->[1];
   $diff_b *= -1 if $diff_b < 0;
   $diff_a <=> $diff_b;
  } @{$dataset->{$col[0]}})[0]->[2];
}