="sourceCode r"><span class="fu">undeclare</span>()</code> proves
useful, and switching between factors and declared objects, preserving
the declared missing values, is now straightforward:</p>
<div class="sourceCode" id="cb16"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="fu"><a href="https://rdrr.io/r/base/factor.html" class="external-link">as.factor</a></span><span class="op">(</span><span class="fu"><a href="../reference/drop_undeclare.html">undeclare</a></span><span c