code: public static TupleDesc_F64 combine( List<TupleDesc_F64> inputs , TupleDesc_F64 combined ) {
  		int N = 0;
  		for (int i = 0; i < inputs.size(); i++) {
  			N += inputs.get(i).size();
  		}
  		if( combined == null ) {
  			combined = new TupleDesc_F64(N);
  		} else {
  			if (N != combined.size())
  				throw new RuntimeException("The combined feature needs to be " + N + "  not " + combined.size());
  		}
  
  		int start = 0;
  		for (int i = 0; i < inputs.size(); i++) {
  			double v[] = inputs.get(i).value;
  			System.arraycopy(v,0,combined.value,start,v.length);
  			start += v.length;
  		}
  
  		return combined;
  	}
docs: Concats the list of tuples together into one big feature.  The combined feature must be large
  enough to store all the inputs.
  
  @param inputs List of tuples.
  @param combined Storage for combined output.  If null a new instance will be declared.
  @return Resulting combined.