title: Accessing the values of the reduced dataset after facet_grid in ggplot
body: <p>Building on <a href="https://stackoverflow.com/q/66752860/6708910">this earlier</a> question, let's say the data table has columns <code>ID,factor,SimulationID,Data</code>. During the plotting, we want to plot a new graph. for each <code>(factor, SimulationID)</code> tuple using <code>facet_grid()</code>. And for each of these plots, we will use <code>ID</code> varialbe to connect to <code>Data</code> points as a line. However, the set of unique <code>ID</code> values in for each <code>(factor, SimulationID)</code> tuple are different from each other.</p>
  <p>Now, What I want is to highlight one of the curves in each of these plots separated by <code>facet_grid()</code>.</p>
  <pre><code>ggplot(d) +
  facet_grid(factor~SimulationID,)+
    geom_line(aes(idx, value, colour = type)) +
    gghighlight(ID == &lt;choose a valid ID randomly&gt;)
  </code></pre>