tention to summarise down the <code>val</code> column,
set <code>.summarise = TRUE</code> in the call to
<code><a href="../reference/sum_byname.html">sum_byname()</a></code>. Note that
<code>sum_byname(.summarise = TRUE)</code> <em>always</em> returns a
list column, because if the summarised column were to contain matrices,
it <em>must</em> be a list column.</p>
<div class="sourceCode" id="cb20"><pre class="downlit sourceCode r">
<code class="sourceCode R"><span><span class="va">res</span> <span class="op">