Polynomial Combination

Polynomial combination.:

>>> from featurebox.featurizers.state.union import PolyFeature
>>> n = np.array([[0,1,2,3,4,5],[0.422068,0.360958,0.201433,-0.459164,-0.064783,-0.250939]]).T
>>> ps = pd.DataFrame(n,columns=["f1","f2"],index= ["x0","x1","x2","x3","x4","x5"])
>>> pf = PolyFeature(degree=[1,2])
>>> pf.fit_transform(n)

   f0^1      f1^1  f0^2  f0^1*f1^1      f1^2  ...
0   0.0  0.422068   0.0   0.000000  0.178141  ...
1   1.0  0.360958   1.0   0.360958  0.130291  ...
2   2.0  0.201433   4.0   0.402866  0.040575  ...
3   3.0 -0.459164   9.0  -1.377492  0.210832  ...
4   4.0 -0.064783  16.0  -0.259132  0.004197  ...
5   5.0 -0.250939  25.0  -1.254695  0.062970  ...