an>, byrow <span class="op">=</span> <span class="cn">TRUE</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="va">g</span> <span class="op">&lt;-</span> <span class="fu">graph_pairs</span><span class="op">(</span><span class="va">pairs</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="kw">if</span> <span class="op">(</span><span class="va">has_Rgraphviz</span><span class="op">)</span><span class="op">{</span></span></span>
<span class="r-in"