my @sorted_array = 

    map { $_->{line} }  # extract the lines again 

      sort { # do the sorting
             $a->{ts} <=> $b->{ts} || $a->{letter} cmp $b->{letter}
           }  

       map { # build a data-structure that we can sort on
             my ($ts, $letter) = split / /;
             { line => $_, ts => $ts, letter => $letter }
           }   

         @array_to_sort;