n class="fu"><a href="https://r-spatial.github.io/sf/reference/st_zm.html" class="external-link">st_zm</a></span><span class="op">(</span><span class="va">flowlines</span><span class="op">[</span><span class="va">flowlines</span><span class="op">$</span><span class="va">COMID</span> <span class="op"><a href="https://rdrr.io/r/base/match.html" class="external-link">%in%</a></span> <span class="va">unique_index</span><span class="op">$</span><span class="va">COMID</span>,<span class="op">]</span><span class="