; 5 e       5</span></span>
<span><span class="co">#&gt; 6 f     -91 (NA) [Missing]</span></span>
<span><span class="co">#&gt; 7 g     -91 (NA) [Missing]</span></span></code></pre></div>
<p>Special challenges are associated with sorting and ordering the
declared objects, where not all missing values are treated the same.</p>
<div class="sourceCode" id="cb10"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">x3</span> <span class="op">&lt;-</span> <span class="fu"><a href="