从动物园提取月和年::年目标

I have a yearmon object:

我有一个共同的目标:

require(zoo)
date1 <- as.yearmon("Mar 2012", "%b %Y")
class(date1)
# [1] "yearmon"

How can I extract the month and year from this?

我如何从中提取月和年?

month1 <- fn(date1)
year1 <- fn(date1)

What function should I use in place of fn()

用什么函数代替fn()

6 个解决方案

#1

134

Use the format() method for objects of class "yearmon". Here is your example date (properly created!)

对于类“yearmon”的对象使用format()方法。这是您的示例日期(正确创建!)

date1 <- as.yearmon("Mar 2012", "%b %Y")

Then we can extract the date parts as required:

然后根据需要提取日期部分:

> format(date1, "%b") ## Month, char, abbreviated
[1] "Mar"
> format(date1, "%Y") ## Year with century
[1] "2012"
> format(date1, "%m") ## numeric month
[1] "03"

These are returned as characters. Where appropriate, wrap in as.numeric() if you want the year or numeric month as a numeric variable, e.g.

它们作为字符返回。如果需要将年份或数字月作为数值变量，请在适当的地方使用asn .numeric()包装。

> as.numeric(format(date1, "%m"))
[1] 3
> as.numeric(format(date1, "%Y"))
[1] 2012

See ?yearmon and ?strftime for details - the latter explains the placeholder characters you can use.

参见yearmon和?strftime获取详细信息——后者解释了您可以使用的占位符。

#2

The lubridate package is amazing for this kind of thing:

这类产品的润滑包装非常棒:

> require(lubridate)
> month(date1)
[1] 3
> year(date1)
[1] 2012

#3

I know the OP is using zoo here, but I found this thread googling for a standard ts solution for the same problem. So I thought I'd add a zoo-free answer for ts as well.

我知道OP在这里使用zoo，但是我发现这个线程在google上搜索同样的问题的标准ts解决方案。所以我想我应该为ts添加一个无动物的答案。

# create an example Date 
date_1 <- as.Date("1990-01-01")
# extract year
as.numeric(format(date_1, "%Y"))
# extract month
as.numeric(format(date_1, "%m"))

#4

You can use format:

您可以使用格式:

library(zoo)
x <- as.yearmon(Sys.time())
format(x,"%b")
[1] "Mar"
format(x,"%Y")
[1] "2012"

#5

For large vectors:

对于大型向量:

y = as.POSIXlt(date1)$year + 1900    # x$year : years since 1900
m = as.POSIXlt(date1)$mon + 1        # x$mon : 0–11

#6

The question did not state precisely what output is expected but assuming that for month you want the month number (January = 1) and for the year you want the numeric 4 digit year then assuming that we have just run the code in the question:

问题并没有明确说明预期的输出，但假设您想要一个月的月号(1月= 1)，而想要数字4位数的年，那么假设我们刚刚运行了问题中的代码:

cycle(date1)
## [1] 3
as.integer(date1)
## [1] 2012

#1

134