code: public ConcatVectorTableProto.ConcatVectorTable.Builder getProtoBuilder() {
          ConcatVectorTableProto.ConcatVectorTable.Builder b = ConcatVectorTableProto.ConcatVectorTable.newBuilder();
          for (int n : getDimensions()) {
              b.addDimensionSize(n);
          }
          for (int[] assignment : this) {
              b.addFactorTable(getAssignmentValue(assignment).get().getProtoBuilder());
          }
          return b;
      }
docs: Returns the proto builder object for this feature factor. Recursively constructs protos for all the concat
  vectors in factorTable.
  
  @return proto Builder object