name,
                                       clojure.lang.IFn&nbsp;perElemFn,
                                       clojure.lang.IFn&nbsp;finalizeFn)</pre>
<div class="block"><p>Create a custom reducer. perElemFn is passed the last return value as the first argument followed by a value from each column as additional arguments. It must always return the current context.</p>
<p>This is a easy way to instantiate tech.v3.datatype.IndexReduction so if you really need the best possible performance you need to im