我有两列PosixLT时间没有NA值，但是在检查时会显示NA值
> sum(is.na(check$start))
[1] 19
> sum(is.na(check$end))
[1] 23
数据存在于单元格中，为什么会发生这种情况？我听说PosixLT会发生这种情况，但即使我将其转换为posixCT，也会有非常奇怪的行为。如何解决这个问题？
> as.POSIXct(check$start, format = "%Y-%m-%d %H:%M:%S", tz = "CST6CDT")
[1] NA "2014-03-09 01:35:01 CST" NA "2014-03-09 01:53:30 CST" NA
[6] NA NA NA NA "2014-03-09 04:17:11 CDT"
[11] NA NA "2015-03-08 01:54:43 CST" NA NA
[16] NA NA NA NA NA
[21] NA NA NA
> dput(check)
structure(list(start = structure(list(sec = c(24, 1, 27, 30,
8, 21, 40, 9, 43, 11, 31, 43, 43, 55, 39, 54, 41, 19, 2, 35,
6, 54, 40), min = c(45L, 35L, 14L, 53L, 36L, 37L, 47L, 48L, 54L,
17L, 57L, 53L, 54L, 3L, 52L, 22L, 34L, 28L, 41L, 42L, 52L, 52L,
53L), hour = c(2L, 1L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 4L, 2L, 2L,
1L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L), mday = c(9L, 9L,
9L, 9L, 9L, 9L, 9L, 9L, 9L, 9L, 9L, 8L, 8L, 8L, 8L, 8L, 8L, 8L,
8L, 8L, 8L, 8L, 8L), mon = c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L),
year = c(114L, 114L, 114L, 114L, 114L, 114L, 114L, 114L,
114L, 114L, 114L, 115L, 115L, 115L, 115L, 115L, 115L, 115L,
115L, 115L, 115L, 115L, 115L), wday = c(0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L), yday = c(67L, 67L, 67L, 67L, 67L, 67L, 67L,
67L, 67L, 67L, 67L, 66L, 66L, 66L, 66L, 66L, 66L, 66L, 66L,
66L, 66L, 66L, 66L), isdst = c(-1L, 0L, -1L, 0L, -1L, -1L,
-1L, -1L, -1L, 1L, -1L, -1L, 0L, -1L, -1L, -1L, -1L, -1L,
-1L, -1L, -1L, -1L, -1L), zone = c("", "CST", "", "CST",
"", "", "", "", "", "CDT", "", "", "CST", "", "", "", "",
"", "", "", "", "", ""), gmtoff = c(NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_)), .Names = c("sec", "min", "hour", "mday", "mon",
"year", "wday", "yday", "isdst", "zone", "gmtoff"), class = c("POSIXlt",
"POSIXt"), tzone = c("CST6CDT", "CST", "CDT")), end = structure(list(
sec = c(7, 59, 38, 45, 29, 46, 39, 14, 52, 29, 37, 5, 23,
41, 10, 43, 46, 46, 53, 24, 57, 13, 51), min = c(55L, 47L,
30L, 2L, 43L, 51L, 53L, 56L, 54L, 54L, 57L, 56L, 6L, 3L,
13L, 29L, 37L, 32L, 48L, 47L, 55L, 55L, 55L), hour = c(2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L), mday = c(9L, 9L, 9L, 9L, 9L,
9L, 9L, 9L, 9L, 9L, 9L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L,
8L, 8L, 8L), mon = c(2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L),
year = c(114L, 114L, 114L, 114L, 114L, 114L, 114L, 114L,
114L, 114L, 114L, 115L, 115L, 115L, 115L, 115L, 115L, 115L,
115L, 115L, 115L, 115L, 115L), wday = c(0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L, 0L,
0L, 0L, 0L), yday = c(67L, 67L, 67L, 67L, 67L, 67L, 67L,
67L, 67L, 67L, 67L, 66L, 66L, 66L, 66L, 66L, 66L, 66L, 66L,
66L, 66L, 66L, 66L), isdst = c(-1L, -1L, -1L, -1L, -1L, -1L,
-1L, -1L, -1L, -1L, -1L, -1L, -1L, -1L, -1L, -1L, -1L, -1L,
-1L, -1L, -1L, -1L, -1L), zone = c("", "", "", "", "", "",
"", "", "", "", "", "", "", "", "", "", "", "", "", "", "",
"", ""), gmtoff = c(NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_,
NA_integer_, NA_integer_, NA_integer_, NA_integer_, NA_integer_
)), .Names = c("sec", "min", "hour", "mday", "mon", "year",
"wday", "yday", "isdst", "zone", "gmtoff"), class = c("POSIXlt",
"POSIXt"), tzone = c("CST6CDT", "CST", "CDT"))), .Names = c("start",
"end"), row.names = c(1559963L, 1560092L, 1560157L, 1560220L,
1560240L, 1560247L, 1560252L, 1560253L, 1560255L, 1560258L, 1560260L,
2004432L, 2004583L, 2004591L, 2004594L, 2004596L, 2004598L, 2004599L,
2004600L, 2004603L, 2004609L, 2004610L, 2004611L), class = "data.frame")
答案 0 :(得分：8)
在这种情况下如何运作is.na？
> is.na.POSIXlt
function (x)
is.na(as.POSIXct(x))
<bytecode: 0x0000000014232980>
as.POSIXct如何在这里表现？
> as.POSIXct(check$start)
[1] NA "2014-03-09 01:35:01 CST" NA "2014-03-09 01:53:30 CST"
[5] NA NA NA NA
[9] NA "2014-03-09 04:17:11 CDT" NA NA
[13] "2015-03-08 01:54:43 CST" NA NA NA
[17] NA NA NA NA
[21] NA NA NA
好的，但为什么????
让我们查看as.POSIXct的文档：
需要在两个日期时间类之间进行的任何转换 需要一个时区：转换自＆＃34; POSIXlt＆＃34;到＆＃34; POSIXct＆＃34;将 验证所选时区的时间。一个问题是发生了什么 转入和转出DST，例如在英国
让我们看看：
> check$start$zone
[1] "" "CST" "" "CST" "" "" "" "" "" "CDT" "" "" "CST" "" "" "" "" "" "" ""
[21] "" "" ""
这里有龙，除了4个条目外没有时区，所以as.POSIXct无法判断日期是否有效（在DST更改内是否？）你可以看到：
> check$start$isdst
[1] -1 0 -1 0 -1 -1 -1 -1 -1 1 -1 -1 0 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
因此POSIXlt（您的数据帧）和POSIXct之间的转换无法猜测日期是否有效，并返回NA。
一种修复方法可能是对所有记录强制执行时区：
> check$start <- as.POSIXlt(strftime(check$start,tz="CST"),tz="CST6CDT")
> is.na(check$start)
[1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE