String field = w.getField().toExpr();
if ( ! combinedVectors.containsKey(field)) {
MaterializedField mf = w.getField();
ValueVector[] vvList = (ValueVector[]) Array.newInstance(mf.getValueClass(), 1);
vvList[0] = w.getValueVector();
combinedVectors.put(mf.getPath().toExpr(), new HyperVectorValueIterator(mf, new HyperVectorWrapper(mf,
vvList)));
} else {
combinedVectors.get(field).hyperVector.addVector(w.getValueVector());
}