title: Add last filled field in column (r language)
body: <p>I have my table (input):</p>
  
  <pre><code>user_id  level1 level2 level3 level4
  Rob      123456 456456 NA     12345
  Mike     23445  NA     NA     NA
  Stan     23423  345345 NA     NA
  </code></pre>
  
  <p>And I want to create column with last <code>levelName</code> that has value (output):</p>
  
  <pre><code>user_id  level1 level2 level3 level4  lastLevel
  Rob      123456 456456 NA     12345   level4
  Mike     23445  NA     NA     NA      level1
  Stan     23423  345345 NA     NA      level2
  </code></pre>
  
  <p>THX!</p>