def best_result_df(grid_search_df):
    """
    Select optimal order for ARIMA model from dataframe of valid fits

    Args:
        grid_search_df: pandas dataframe of valid ARIMA estimators' parameters

    Returns:
        best_result_df: pandas dataframe of row with optimal order based on AIC

    """
    best_result_df = grid_search_df[grid_search_df.aic == grid_search_df.aic.min()]

    return best_result_df