减少月份 - 与最后一个月的问题？ [英] Subtracting months - issue with last day of month?

问题描述

在R中的日期的快速问题。查看这段代码：

Quick question on dates in R. Check out this snippet of code:

Sys.Date() - months(3)
# [1] "2013-12-31"
Sys.Date() - months(18)
# [1] NA

我已经加载了 lubridate ，并按照提供的说明，我不能完全弄清楚这个行为。以前工作很好，今天是第一天，我注意到从今天起扣减了12个月以上，收到 NA （扣除少于12个月的工作正常）

I've loaded the package lubridate and followed the instructions provided , and I can't quite get my head around this behavior. It used to work just fine, today's the first day that I've noticed that a subtraction of more than 12 months from today's date yields NA (subtracting less than 12 months works fine).

如果有人可以向我解释为什么这不工作，和/或建议一个更强壮的方式，我将不胜感激。这是否与今天的最后一天（第31天）有关？

I'd appreciate if anyone can explain to me why this isn't working, and/or suggest a more "robust" way around it. Does it have something to do with today being the last day of the month (day 31)?

我问这是因为这样做：

Sys.Date() - years(2)
# [1] "2012-03-31"

推荐答案

lubridate $ c>％m +％和％m - ％旨在处理此问题（添加和减去几个月到不超过最后

The lubridate functions %m+% and %m-% are designed to handle this issue ("Add and subtract months to a date without exceeding the last day of the new month").

library(lubridate)
Sys.Date() %m-% months(18)
# [1] "2012-09-30"

# or to make it reproducible if Sys.Date() happens to be different from that in OP
as.Date("2014-03-31") %m-% months(18)
# [1] "2012-09-30"

# example of %m+%
as.Date("2014-01-31") + months(1)
# [1] NA
as.Date("2014-01-31") %m+% months(1)
# [1] "2014-02-28"

这篇关于减少月份 - 与最后一个月的问题？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！