日期时间范围中前一天/月/年的第一个可用日期 [英] First available date previous day/month/year from a datetime range

问题描述

我有一个带有日期(dfDates)的datetime实例:

I have a datetime instance with dates (dfDates):

2017-03-01 00:00
2017-03-02 00:00
2017-03-04 00:00
...

对于最后一天(在这里:2017-03-04)，我计算前一天/月/年/等.如下:

For the last day (here: 2017-03-04) I calculate the previous day/month/year/etc. as follows:

def previous_day(dtToday):
    return dtToday - pd.DateOffset(days=1)

这将返回2017-03-03.但是，该工作日在我的日期范围(dfDates)中不可用.

This returns 2017-03-03. However, this business day is not available in my range of dates (dfDates).

因此，我正在寻找一种可靠的方法来查找最接近前一天/月/年/等的日期.在这种情况下，前一天应该返回2017-03-02.

I am therefore looking for a robust way to find the date that is the closest to the previous day/month/year/etc.. In this case for the previous day it should return 2017-03-02.

请注意，我了解您可以执行类似索引-1的操作来获取前一天.但是，如果使用上个月(一个月中并非总是30天)甚至是上一年(一年中并不总是有252个工作日)，则变得非常复杂.因此，是否有一种健壮的方法来获取最接近的可用日期?

Note, I understand that you can do something like index -1 to get the previous day. It becomes however complicated when taking the previous month (there are not always 30 days in a month) and even the previous year (there are not always 252 working days in a year). Is there therefore a robust method to get the closest available date?

更新

我也了解您可以按以下方式使用timedelta:

I understand also that you can use timedelta as follows:

from datetime import datetime, timedelta

d = datetime.today() - timedelta(days=days_to_subtract)

但是，这与dtToday有什么关系，如何将其与dfDates链接?在我的情况下，dtToday并不总是datetime.today().有时是随机日期.

However, how does that relate to dtToday and how can I link it with dfDates? dtToday in my case is not always datetime.today(). Sometimes its a random date.

推荐答案

我是这样解决的:

• dtToday =参考日期
• dtDates =日期的时间序列 可用日期
• nbOffset =我们想要的天数/月数/年数 回去

• dtToday = the reference date
• dtDates = a datetime sequence of the available dates
• nbOffset = the number of days/months/years we want to go back

代码:

def previous_day(dtToday, dtDates, nbOffset):
    prevx   = dtToday - pd.DateOffset(days=nbOffset)
    return test_day_in(prevx, dtDates)

def previous_month(dtToday, dtDates, nbOffset):
    prevx = dtToday - pd.DateOffset(months=nbOffset)
    return test_day_in(prevx, dtDates)

def previous_year(dtToday, dtDates, nbOffset):
    prevx = dtToday - pd.DateOffset(years=nbOffset)
    return test_day_in(prevx, dtDates)

def test_day_in(dtTest, dtDates):
    if dtTest in dtDates:
        return dtTest
    else:
        return tryNextDay(dtTest, dtDates)

def tryNextDay(dtTest, dtDates):

    # if not outside the bound
    if (dtTest < dtDates.min()):
        return dtDates.min()

    # check if next day exist
    if (dtTest + pd.DateOffset(days=1) <= dtDates.max()):
        return previous_day(dtTest + pd.DateOffset(days=2), dtDates, 1) # 2-1
    else:
        print('warning, tryNextDay triggered')
        # should not be triggered, it should take by default the dtDates.min() if far outside range
        return dtTest

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