a-check"></i><b>17.4.11</b> is_na()</a></li>
</ul></li>
<li class="chapter" data-level="17.5" data-path="190_datetime.html"><a href="190_datetime.html#code-example-datetime"><i class="fa fa-check"></i><b>17.5</b> Code example</a></li>
</ul></li>
<li class="chapter" data-level="18" data-path="200_robject.html"><a href="200_robject.html"><i class="fa fa-check"></i><b>18</b> RObject</a>
<ul>
<li class="chapter" data-level="18.1" data-path="200_robject.html"><a href="200_robject.html#member-functions"><i class=