bject, will override the plot
data. All objects will be fortified to produce a data frame. See
<code><a href="https://ggplot2.tidyverse.org/reference/fortify.html" class="external-link">fortify()</a></code> for which variables will be created.</p>
<p>A <code>function</code> will be called with a single argument,
the plot data. The return value must be a <code>data.frame</code>, and
will be used as the layer data. A <code>function</code> can be created
from a <code>formula</code> (e.g. <code>~ head(.x, 10)</