def _get_nn_idx(row, neigh, radius, columns):
    """Retrieve the NN of a sample within a specified radius.

    Parameters
    ----------
    row : pd.Series
    neigh : sklearn.NearestNeighbors
    radius : float
    columns : list

    Returns
    -------
    list
        Nearest Neighbors of given sample within radius
    """
    neigh_dist, neigh_idx = neigh.radius_neighbors([row[columns]], radius)
    return neigh_idx[0], len(neigh_idx[0])