Question

我在R中有一个数据框，还有一个名为created_at的列，它包含一个我要解析为日期时间的文本。这是一个快速预览：

head(pushes)

    created_at repo.url                                  repository.url

1 2013-06-17T00:14:04Z                          https://github.com/Mindful/blog

2 2013-07-31T21:08:15Z          https://github.com/leapmotion/js.leapmotion.com

3 2012-11-04T07:08:15Z                       https://github.com/jplusui/jplusui

4 2012-06-21T08:16:22Z                  https://github.com/LStuker/puppet-rbenv

5 2013-03-10T09:15:51Z           https://github.com/Fchaubard/CS108FinalProject

6 2013-10-04T11:34:11Z                       https://github.com/cmmurray/soccer

  actor.login payload.actor actor_attributes.login

1                                          Mindful

2                                        joshbuddy

3                                             xuld

4                                          LStuker

5                                         ststanko

6                                         cmmurray

我写了一些适用于某些测试数据的说明：

xts::.parseISO8601("2012-06-17T00:14:04",tz="UTC")$first.time返回正确的Posix日期

但是当我使用此指令将其应用于列时：

pushes$created_at <- xts::.parseISO8601(substr(pushes$created_at,1,nchar(pushes$created_at)-1),tz="UTC")$first.time

数据框中的每一行都有一个重复的日期2012-06-17 00:14:04 UTC

就像第一行只运行一次的函数一样，然后结果在其余行中重复:(请你帮我在created_at列中每行正确应用它？

感谢。

Answer 1

.parseISO8601的第一个参数应该是一个字符串，而不是一个向量。您需要使用sapply（或等效的）来遍历您的向量。

created_at <-
  c("2013-06-17T00:14:04Z", "2013-07-31T21:08:15Z", "2012-11-04T07:08:15Z",
    "2012-06-21T08:16:22Z", "2013-03-10T09:15:51Z", "2013-10-04T11:34:11Z")
# Only parses first element
.parseISO8601(substr(created_at,1,nchar(created_at)-1),tz="UTC")$first.time
# [1] "2013-06-17 00:14:04 UTC"
firstParseISO8601 <- function(x) .parseISO8601(x,tz="UTC")$first.time
# parse all elements
datetimes <- sapply(sub("Z$","",created_at), firstParseISO8601, USE.NAMES=FALSE)
# note that "simplifying" the output strips the POSIXct class, so we re-add it
datetimes <- .POSIXct(datetimes, tz="UTC")

如何在数据帧中每行应用xts函数

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