gation_map</code> and the <code>pattern_type</code>, if
provided. With the default <code>aggregation_map = NULL</code>,
identically named pieces are aggregated together.</p>
<div class="sourceCode" id="cb15"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">m_pieces</span></span>
<span><span class="co">#&gt;                          Motors -&gt; MD Cars -&gt; MD LED lamps -&gt; Light</span></span>
<span><span class="co">#&gt; Electricity [from Coal]             1          