def to_nmatrix
      each_vector.select do |vector|
        vector.numeric? && !vector.include_values?(*Daru::MISSING_VALUES)
      end.map(&:to_a).transpose.to_nm
    end
def to_nmatrix
      each_vector.select do |vector|
        vector.numeric? && !vector.include_values?(*Daru::MISSING_VALUES)
      end.map(&:to_a).transpose.to_nm
    end
:nocov:
 Convert all vectors of type *:numeric* and not containing nils into an NMatrix.