provide no possibility to assign specific values for
the specific categories, and most importantly, they do not differentiate
between valid values and (declared) missing values. To make the
functionality consistent with the base treatment of <code>NA</code>
values, coercing to factors defaults to dropping the declared missing
values because of the default value of the argument <code class="sourceCode r">drop_na</code>:</p>
<div class="sourceCode" id="cb15"><pre class="downlit sourceCode r">
<code class="sou