 frame without <code>.chain</code>, <code>.iteration</code>, and
<code>.draw</code> columns, where all non-grouped columns have been converted to <code><a href="https://mc-stan.org/posterior/reference/rvar.html" class="external-link">rvar</a></code>s.</p>
<p>For <code>unnest_rvars()</code>, returns a data frame with <code>.chain</code>, <code>.iteration</code>, and
<code>.draw</code> columns added, where every <code><a href="https://mc-stan.org/posterior/reference/rvar.html" class="external-link">rvar</a></