code: function calculateActiveConceptIds(item) {
    if (item._concepts.length === 0) {
      return [];
    }
    var conceptItems = item._concepts[0].items;
    return conceptItems.map(parent =>
      // Note this wouldn't work whilst following through on the activeItems knockout subscription,
      // if we hadn't wrapped that in a runLater. You would have had to explicitly call
      // parent.items.filter(concept => concept.isActive).map(concept => concept.id)
      parent.activeItems.map(concept => concept.id)
    );
  }
docs: Map the active concepts into arrays of arrays of ids. Eg. Return [['GDP', 'GNP'], ['Q']].