return new Instance(dest.weight(), vals);
inst = new Instance(dest.weight(), vals);
  protected Instance mergeInstances(Instance source, Instance dest)    throws Exception {    Instances outputFormat = outputFormatPeek();    double[] vals = new double[outputFormat.numAttributes()];    for(int i = 0; i < vals.length; i++) {      if (m_SelectedCols.isInRange(i)) {	if ((source != null)	    && !source.isMissing(i)	    && !dest.isMissing(i)) {	  vals[i] = dest.value(i) - source.value(i);	}      } else {	vals[i] = dest.value(i);      }    }    if (dest instanceof SparseInstance) {      return new SparseInstance(dest.weight(), vals);    } else {      return new Instance(dest.weight(), vals);    }  }