class="op">~</span> <span class="va">group</span> <span class="op">*</span> <span class="va">year</span>, data <span class="op">=</span> <span class="va">DF</span><span class="op">)</span></span></span>
<span class="r-in"><span><span class="va">Z</span> <span class="op">&lt;-</span> <span class="fu"><a href="methods.html">model.matrix</a></span><span class="op">(</span><span class="op">~</span> <span class="va">year</span>, data <span class="op">=</span> <span class="va">DF</span><span class="op">)</span></