如何在R中减去日子？ [英] How to subtract days in R?

问题描述

我正在尝试构建文件夹来存储数据。我想在文件夹的日期标注文件夹。

I'm trying to build folders to store data pulls. I want to label the folders with the day of that data in the pull.

Ex。我拉5天前从mysql的数据我想从5天前命名该文件夹日期。

Ex. I pull 5 days ago data from mysql i want to name the folder the date from 5 days ago.

MySQL可以轻松处理日期算术。我不知道R是如何做的。我应该在POSIXct中减去适当的秒数，然后转换为POSIXlt命名文件夹MM_DD_YYYY？

MySQL can easily handle date arithmetic. I'm not sure exactly how R does it. Should i just subtract the appropriate number of seconds in POSIXct and then convert to POSIXlt to name the folder MM_DD_YYYY?

还是有更好的方法？

推荐答案

只需减去一个数字：

> as.Date("2009-10-01")
[1] "2009-10-01"
> as.Date("2009-10-01")-5
[1] "2009-09-26"

由于 Date 类只有几天，您只需对其进行基本算术。

Since the Date class only has days, you can just do basic arithmetic on it.

如果你想使用POSIXlt，因为某些原因，你可以使用它的插槽：

If you want to use POSIXlt for some reason, then you can use it's slots:

> a <- as.POSIXlt("2009-10-04")
> names(unclass(as.POSIXlt("2009-10-04")))
[1] "sec"   "min"   "hour"  "mday"  "mon"   "year"  "wday"  "yday"  "isdst"
> a$mday <- a$mday - 6
> a
[1] "2009-09-28 EDT"

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