r-in"><span><span class="va">formula</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/stats/formula.html" class="external-link">as.formula</a></span><span class="op">(</span><span class="op">~</span><span class="va">time</span><span class="op">+</span><span class="va">z</span><span class="op">+</span><span class="va">x</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="va">dat</span> <span class="op">&lt