POSIXct 和 sapply 的向量

发布于 2024-09-08 06:23:42 字数 682 浏览 2 评论 0原文

如果您想将 format 以外的函数应用于 POSIXct 对象列表，该怎么办？例如，假设我想获取一个时间向量，将这些时间截断为小时，并对每个时间应用任意函数。

> obs.times=as.POSIXct(c('2010-01-02 12:37:45','2010-01-02 08:45:45','2010-01-09 14:45:53'))
> obs.truncated=trunc(obs.times, units="hours")
> obs.truncated
[1] "2010-01-02 12:00:00 EST" "2010-01-02 08:00:00 EST"
[3] "2010-01-09 14:00:00 EST"

现在，我预计 obs.truncated 的长度为 3，但是

> length(obs.truncated)
[1] 9

您可以看到，尝试将函数应用于此向量是行不通的。 obs.truncated 类是

> class(obs.truncated)
[1] "POSIXt"  "POSIXlt"

知道这里发生了什么吗？ apply 和 length 似乎将向量的第一个元素作为自己的列表。

原文

What if you want to apply a function other than format to a list of POSIXct objects? For instance, say I want to take a vector of times, truncate those times to the hour, and apply an arbitrary function to each one of those times.

> obs.times=as.POSIXct(c('2010-01-02 12:37:45','2010-01-02 08:45:45','2010-01-09 14:45:53'))
> obs.truncated=trunc(obs.times, units="hours")
> obs.truncated
[1] "2010-01-02 12:00:00 EST" "2010-01-02 08:00:00 EST"
[3] "2010-01-09 14:00:00 EST"

Now, I would expect the length of obs.truncated to be 3 but

> length(obs.truncated)
[1] 9

So you can see that trying to apply a function to this vector is not going to work. The class of obs.truncated is

> class(obs.truncated)
[1] "POSIXt"  "POSIXlt"

Any idea what is going on here? apply and length appear to be taking the first element of the vector as its own list.

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好菇凉咱不稀罕他 2024-09-15 06:23:42

这种 POSIXlt 的 length() 过去被报告为 9，但最近得到了更正。

另外，当我执行 trunc(obs.times) 时，会发生错误的事情 - trunc() 只对三个元素的字符串执行一次。你确实需要 apply() 等。

，这里是使用 sapply() 进行组件级重置的示例：

> sapply(obs.times, function(.) {
+ p <- as.POSIXlt(.); 
+ p$min <- p$sec <- 0; 
+ format(p) })
[1] "2010-01-02 12:00:00" "2010-01-02 08:00:00" "2010-01-09 14:00:00"
>

因此

> trunc(obs.times, units="hours")
[1] "2010-01-02 12:00:00 CST" "2010-01-02 08:00:00 CST"
[3] "2010-01-09 14:00:00 CST"
> class(trunc(obs.times, units="hours"))
[1] "POSIXt"  "POSIXlt"
> length(trunc(obs.times, units="hours"))
[1] 1
>

The length() of such a POSIXlt used to be reported as nine, but that got recently corrected.

Also, when I do trunc(obs.times) the wrong thing happens -- trunc() operates only once on a string of three elements. you do need apply() et al.

So here is an example of using sapply() with component-wise resetting:

> sapply(obs.times, function(.) {
+ p <- as.POSIXlt(.); 
+ p$min <- p$sec <- 0; 
+ format(p) })
[1] "2010-01-02 12:00:00" "2010-01-02 08:00:00" "2010-01-09 14:00:00"
>

Whereas

> trunc(obs.times, units="hours")
[1] "2010-01-02 12:00:00 CST" "2010-01-02 08:00:00 CST"
[3] "2010-01-09 14:00:00 CST"
> class(trunc(obs.times, units="hours"))
[1] "POSIXt"  "POSIXlt"
> length(trunc(obs.times, units="hours"))
[1] 1
>

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