title: remove invisible characters from a UTF-8 string
body: <p>I have an R tibble with UTF-8 character column. When I print the contents of this column for a certain problematic record, everything looks fine: <code>one ‭two‬ three</code>. There are, however, problems when I try to use this string in a RDBMS query which I construct in R and send to the database. </p>
  
  <p>If I copy this string to Notepad++ and convert the encoding to ANSI, I can see that the string actually contains some additional characters that cause the problem: <code>one â€­twoâ€¬ three</code>.</p>
  
  <p>A partial solution that works would be conversion to ASCII:
  <code>iconv(my_string, "UTF-8", "ASCII", sub = "")</code>
  , but all non-ASCII characters are lost here.</p>
  
  <p>Conversion from UTF-8 to UTF-8 doesn't solve my problem:
  <code>iconv(my_string, "UTF-8", "UTF-8", sub = "")</code>.</p>
  
  <p>Is it possible to remove <strong>all</strong> invisible characters like the ones above without losing the UTF-8 encoding? 
  That is:
  how can I convert my string to the form that I see when I print it out in R (without hidden parts)?</p>