def recall_single(df, num_of_relevant, query_number):
    """
        This function will calculate the recall of a specific query or of the entire DataFrame
        :param df: DataFrame: Contains tweet ids, their scores, ranks and relevance
        :param num_of_relevant: Integer: number of relevant tweets
        :param query_number: Integer/None that tell on what query_number to evaluate precision or None for the entire DataFrame
        :return: Double - The recall
    """
    df2 = df[df['query'] == query_number]
    return df2['y_true'].sum() / num_of_relevant