Theming rows individually if $rows is a string

I had a problem trying to theme a certain row differently because in the view I was working with, $rows was a string instead of an array. I wanted to theme a certain row differently if a condition was met. I know most things can be done in the Views UI but I couldn't figure out this one like that. I was finally able to do this with yourtheme_preprocess_views_view_unformatted(&$vars) in my template.php file. $rows seemed to still behave like an array there (although it went back to being a string later).

function yourtheme_preprocess_views_view_unformatted(&$vars) {

  if ($vars['view']->name == "name_of_view") {

    $rows = $vars['rows'];

    $newRows = array();

    foreach ($rows as $r) {

      $test = strpos($r, "string_i_looked_for");

        if ($test) {
          $newRows[] = "<hr>$r"; // I needed to put in a divider if the condition was met.
        }

        else {
          $newRows[] = $r;
        }
     }
  $vars['rows'] = $newRows; // So that the array of new rows is what will be sent along.
  } 
}

My actual problem required the divider only in the first instance of the test, so I also used a counter, but I think the example above gives the idea.