def get_rps(data_frame):
    """Calculate RPS for all requests

    Args:
        data_frame (DataFrame): data

    Returns:
        int: Requests per second
    """

    from_date = data_frame.iloc[0].time
    to_date = data_frame.iloc[-1].time
    duration = to_date - from_date
    if duration < 0:
        raise ValueError(
            "Incorrect time values from_date > to_data (%f > %f)" %
            (from_date, to_date)
        )
    if duration == 0:
        duration = 1
    requests_count = data_frame.shape[0]
    return requests_count/duration