title: Plotly R order legend entries
body: <p>Is it possible to order the legend entries in R?</p>
  
  <p>If I e.g. specify a pie chart like this:</p>
  
  <pre><code>  plot_ly(df, labels = Product, values = Patients, type = "pie",
            marker = list(colors = Color), textfont=list(color = "white")) %&gt;%
      layout(legend = list(x = 1, y = 0.5))
  </code></pre>
  
  <p>The legend gets sorted by which Product has the highest number of Patients. I would like the legend to be sorted in alphabetical order by Product.</p>
  
  <p>Is this possible?</p>