op">(</span><span class="va">mask_data</span>, <span class="va">space</span><span class="op">)</span></span></span>
<span class="r-in"><span></span></span>
<span class="r-in"><span><span class="co"># Get coordinates of masked voxels</span></span></span>
<span class="r-in"><span><span class="va">mask_idx</span> <span class="op">&lt;-</span> <span class="fu"><a href="https://rdrr.io/r/base/which.html" class="external-link">which</a></span><span class="op">(</span><span class="va">mask_data</span><span class="