>, keep <span class="op">=</span> <span class="cn">TRUE</span>, list_columns <span class="op">=</span> <span class="st">"val"</span> <span class="op">)</span></span></span>
<span class="r-out co"><span class="r-pr">#&gt;</span>   line_id line_id  val   geometry</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 1       1       1 a, b 1, 2, 4, 3</span>
<span class="r-out co"><span class="r-pr">#&gt;</span> 2       2       2 c, d 3, 4, 2, 1</span>
<span class="r-in"><span></span></span>
<span class