an><span class="va">group</span>,</span></span>
<span class="r-in"><span>                    ace <span class="op">=</span> <span class="cn">NULL</span><span class="op">)</span></span></span>
<span class="r-out co"><span class="r-pr">#&gt;</span> </span>
<span class="r-out co"><span class="r-pr">#&gt;</span>  Frequency distribution of path length from X to Y :</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>  1  2  3  4  5 </span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 45 21