@classmethod
def _filter_matrix_rows(cls, matrix):
    """matrix = output from _to_matrix"""
    indexes_to_keep = []
    for i in range(len(matrix)):
        keep_row = False
        for element in matrix[i]:
            if element not in {'NA', 'no'}:
                keep_row = True
                break
        if keep_row:
            indexes_to_keep.append(i)
    return [matrix[i] for i in indexes_to_keep]
