my @cases=();
my @FILE=<DATA>;
close(DATA);

my $num_lines=scalar(@FILE);

$#cases=$num_lines; #pre-extend array

foreach my $line (@FILE) {
   if (($dot % 1000) == 0) {
      print STDERR ".";
   }

   $line=~/^(\S*) [0-9.]* (.*)$/o;
   my ($class, $feature_vector) = ($1, $2); 
   my %case;
    
   $case{'class'}=$class;

   foreach my $feature (split /\s+/, $feature_vector) {
      $case{'fv'}{$feature}=1;
   }

   push @cases, \%case;
   $dot++;
}