/../tech/v3/dataset/Reductions.html#reducer-java.lang.Object-clojure.lang.IFn-clojure.lang.IFn-">reducer</a></span>(java.lang.Object&nbsp;colname,
       clojure.lang.IFn&nbsp;perElemFn,
       clojure.lang.IFn&nbsp;finalizeFn)</code>
<div class="block">Create a custom reducer.</div>
</td>
</tr>
<tr id="i19" class="rowColor">
<td class="colFirst"><code>static java.lang.Object</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../tech/v3/dataset/Reductions.html#reservoirDataset