title: (igraph) Grouped layout based on attribute
body: <p>I'm using the iGraph package in R to layout a network graph, and I would like to group the vertex coordinates based on attribute values.  </p>
  
  <p>Similar to the answered question <a href="https://stackoverflow.com/questions/16390221/how-to-make-grouped-layout-in-igraph">How to make grouped layout in igraph?</a>, my question differs in that the nodes needn't be grouped by a community membership that was derived from a community detection algorithm.</p>
  
  <p>Rather, I want to layout with groups based on attribute values that are known in advance for each vertex.  </p>
  
  <p>For example, if each vertex has an attribute "Master.Org", and there are ~10 to ~20 distinct values for Master.Org, then how can I layout the graph such that all vertices within the same Master.Org are grouped ?</p>
  
  <p>Thanks!</p>
  
  <p><strong>Additional Detail</strong></p>
  
  <p>In fact, two separate attributes provide nested levels of grouping.</p>
  
  <p>My goal is to layout a graph object such that the "Master.Org" and "Org.Of" values are grouped together in their XY coordinates on the graph.  </p>
  
  <p>For example, each node will belong to an "Org.Of".  And there can be multiple "Org.Of" values within the "Master.Org".</p>
  
  <p>Thoughts ?
  Thanks!</p>