my %statistics = (
  1 => [ "foo", "bar" ],
  2 => [ "baz", "bletch" ],
  3 => [ "quux" ],
);

##</code><code>##

    # if we havent hit this line yet, add an array 
    # reference to %statistics at this line number.
    if (not defined $statistics{$line_number} ) { 
      $statistics{$line_number} = [ $thisline ];
    }
    # if we have hit this line, then we have an 
    # array reference already and all we have to do 
    # is push it.
    if (defined $statistics{$line_number} ) {
      push @{ $statistics{$line_number} }, $thisline;
    }