 ony within any given column.</p><p>The row index, column index, and constituent value data are all backed ultimately
by arrays.</p><p><code>Frame</code> is effectively a doubly-indexed associative map whose row keys and col keys
each have an ordering provided by the natural (provided) order of their backing
arrays.</p><p>Several factory and access methods are provided. In the following examples, assume
that:</p><pre><span class="kw">val</span> f = Frame(<span class="lit">'a'</span>-&gt;Vec(<span class="num