use strict;
use warnings;
use Data::Dumper;

my %results;   #pick a better name for this!!

my $eof_seen = 0;
while (!$eof_seen)
{
   
   my %record = get_record();
   
   my ($solvent) = grep {/^solvent/ and $record{$_}==0}keys %record;
   
   foreach my $F (grep {/^F/}keys %record)
   {
      $results{$solvent."_".$F}= $record{$F};
   }
   
   $eof_seen=1 if (eof(DATA));
}
print Dumper \%results;


sub get_record  #blank line separated records
{
   my %record;
   my $line;
   
   while (defined ($line = <DATA>) and $line !~ /^\s*$/)
   {
       my ($key, $value) = split ' ',$line;
       $record{$key} = $value;
   }
   
   return %record;
}

=Prints
$VAR1 = {
          'solvent1_F101' => '3.2',
          'solvent1_F001' => '1.2',
          'solvent2_F101' => '7.2',
          'solvent2_F001' => '2.2'
        };
=cut

   

__DATA__
F001            1.2
F101            3.2
solvent1      0
solvent2     3

F001            2.2
F101            7.2
solvent1      5
solvent2     0