 missing entries, and it is <a href="https://tidyr.tidyverse.org/articles/tidy-data.html" class="external-link">tidy</a>. But
the data are not organized as matrices, and additional metadata is
needed.</p>
<p>The <code>collapse_to_matrices</code> function converts a tidy data
frame into a <code>matsindf</code> data frame using using information
within the tidy data frame. So the first task is to prepare for
<em>collapse</em> by adding metadata columns.</p>
<p><code>collapse_to_matrices</code> needs the follo