he resulting dataset will have one row per grouped key. Columns used as keys will always be represented in the result.</p></div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>dsSeq</code> - Sequence of datasets such as produced by rowMapcat, dsPmap, or loading many files.</dd>
<dd><code>colname</code> - Either a single column name or a vector of column names. These will be the grouping keys.</dd>
<dd><code>aggMap</code> - Map of result colname to reducer. Various reducers are provided 