def get_unique_R(self, R):
        """Get unique vlaues from coordinate matrix

        Parameters
        ----------
        R :  2D array
           The coordinate matrix of a subject's fMRI data

        Return
        ------

        unique_R : a list of array,
            Each element contains unique value in one dimension of
            coordinate matrix R.

        inds : a list of array,
            Each element contains the indices to reconstruct one
            dimension of original cooridnate matrix from the unique
            array.

        """
        unique_R = []
        inds = []
        for d in np.arange(self.n_dim):
            tmp_unique, tmp_inds = np.unique(R[:, d], return_inverse=True)
            unique_R.append(tmp_unique)
            inds.append(tmp_inds)
        return unique_R, inds
Get unique vlaues from coordinate matrix

        Parameters
        ----------
        R :  2D array
           The coordinate matrix of a subject's fMRI data

        Return
        ------

        unique_R : a list of array,
            Each element contains unique value in one dimension of
            coordinate matrix R.

        inds : a list of array,
            Each element contains the indices to reconstruct one
            dimension of original cooridnate matrix from the unique
            array.