span><span class="fl">91</span></span>
<span><span class="op">)</span></span></code></pre></div>
<p>The proposed method to declare missing values is unique in the R
ecosystem. Differentiating between empty and declared missing values
opens the door to a new set of challenges for which base R does not have
built-in functionality.</p>
<p>For instance, the declared missing values can be compared against
both the original values and their labels:</p>
<div class="sourceCode" id="cb2"><pre class="downlit sourceCo