osaic plots do not have a
one-to-one mapping between a variable and the <code>x</code> or
<code>y</code> axis. To accommodate the variable number of variables,
the mapping to <code>x</code> is created by the <code><a href="../reference/product.html">product()</a></code>
function. For example, the variables <code>var1</code> and
<code>var2</code> are read in as <code>x = product(var2, var1)</code>.
The <code><a href="../reference/product.html">product()</a></code> function alludes to
<strong>ggmosaic</strong