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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def partial_transform(self, traj):
 """Featurize an MD trajectory into a vector space with the raw cartesian coordinates. Parameters traj : mdtraj.Trajectory A molecular dynamics trajectory to featurize. Returns ------- features : np.ndarray, dtype=float, shape=(n_samples, n_features) A featurized trajectory is a 2D array of shape `(length_of_trajectory x n_features)` where each `features[i]` vector is computed by applying the featurization function to the `i`th snapshot of the input trajectory. Notes ----- If you requested superposition (gave `ref_traj` in __init__) the input trajectory will be modified. See Also -------- transform : simultaneously featurize a collection of MD trajectories """

        # Optionally take only certain atoms
        if self.atom_indices is not None:
            p_traj = traj.atom_slice(self.atom_indices)
        else:
            p_traj = traj

        # Optionally superpose to a reference trajectory.
        if self.ref_traj is not None:
            p_traj.superpose(self.ref_traj, parallel=False)

        # Get the positions and reshape.
        value = p_traj.xyz.reshape(len(p_traj), -1)
        return value