title: In QGIS I want to display a piechart per region not per country
body: <p>Mac OS X 10.9
  QGIS 2.4</p>
  
  <p>I have a shapefile for the world.
  For each country it has the UN designated subregion code.
  I have some external data that maps to that subregion code.
  I want to show that as a piechart superimposed on the map.</p>
  
  <p>I have added as vector layer, joined on the subregion attribute.
  Then I do: Properties > Diagram > Display Pie Chart</p>
  
  <p>Problem is that because the Data links to each country in the subregion I get N piecharts per region - because the shapefile is country level but the external data is region level (I have country level but just much too messy to display 200 pie charts!)</p>
  
  <p>e.g
  There are 10 countries with subregion code for West Africa so when I join the external data and then display it I get the same all-West-Africa Pie chart displayed 10 times over each individual country.</p>
  
  <p>I just want to display 1 pie chart for West Africa, 1 for East Africa etc., etc.</p>