两个日期之间的月数 [英] Number of months between two dates

问题描述

有没有一个标准/常用的方法/公式来计算R中两个日期之间的月份数？

Is there a standard/common method/formula to calculate the number of months between two dates in R?

我正在寻找类似于 MathWorks月份功能

推荐答案

我刚才说的很简单，但在几周内， difftime（）停止。多么奇怪

I was about to say that's simple, but difftime() stops at weeks. How odd.

所以一个可能的答案就是把这些东西搞砸了：

So one possible answer would be to hack something up:

# turn a date into a 'monthnumber' relative to an origin
R> monnb <- function(d) { lt <- as.POSIXlt(as.Date(d, origin="1900-01-01")); \
                          lt$year*12 + lt$mon } 
# compute a month difference as a difference between two monnb's
R> mondf <- function(d1, d2) { monnb(d2) - monnb(d1) }
# take it for a spin
R> mondf(as.Date("2008-01-01"), Sys.Date())
[1] 24
R> 

似乎是正确的。可以将它包装成一些简单的类结构。或者将其作为一个黑客：）

Seems about right. One could wrap this into some simple class structure. Or leave it as a hack :)

编辑：也似乎适用于Mathworks中的示例：

Also seems to work with your examples from the Mathworks:

R> mondf("2000-05-31", "2000-06-30")
[1] 1
R> mondf(c("2002-03-31", "2002-04-30", "2002-05-31"), "2002-06-30")
[1] 3 2 1
R> 

添加 EndOfMonth 标志留作练习给读者：）

Adding the EndOfMonth flag is left as an exercise to the reader :)

编辑2：可能 difftime 将其作为没有可靠的方式来表达分数差异，这与其他单位的 difftime 行为一致。

Edit 2: Maybe difftime leaves it out as there is no reliable way to express fractional difference which would be consistent with the difftime behavior for other units.

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