我有这样的数据：
View(dose_merged)
SUBJECT_Blinded PACKID SACDPDAT SACRTDAT treatment_interval SD_SDAT SD_EDAT
1 1501301 10094 2012-05-26 2012-07-23 58 2012-01-03 2013-01-02
2 1601301 10555 2012-01-03 2012-01-31 28 2012-01-03 2013-01-0
使用数据表中的列类型：
> mapply(class, dose_merged)
$SUBJECT_Blinded
[1] "numeric"
$PACKID
[1] "numeric"
$SACDPDAT
[1] "POSIXct" "POSIXt"
$SACRTDAT
[1] "POSIXct" "POSIXt"
$treatment_interval
[1] "Interval"
attr(,"package")
[1] "lubridate"
$SD_SDAT
[1] "POSIXct" "POSIXt"
$SD_EDAT
[1] "POSIXct" "POSIXt"
我想确定间隔的交叉长度：间隔（SACDPDAT，SACRTDAT）和间隔（SD_SDAT，SD_EDAT）。 我正在尝试这个：
dose_merged[,intersect1 := aaply(dose_merged, 1, function(x){intersect(interval(x[3],x[4]), interval(x[8],x[9]))})]
但后来我收到错误消息：
Error: error while computing 'x' when choosing method for 'intersect': Error in as.POSIXct.default(start) :
do not know how to convert 'start' to class “POSIXct”
该行
intersect(interval(x[3],x[4]), interval(x[8],x[9]))})
适用于指定的行x。 我有什么想法吗？
前两行dput（dose_merge）：
structure(list(SUBJECT_Blinded = c(1101001, 1101001), PACKID = c(10096,
10595), SACDPDAT = structure(c(1335304800, 1325545200), class = c("POSIXct",
"POSIXt"), tzone = ""), SACRTDAT = structure(c(1340316000, 1327964400
), class = c("POSIXct", "POSIXt"), tzone = ""), treatment_interval = structure(c(58,
28), class = structure("Interval", package = "lubridate")), TS_SDAT = structure(c(NA_real_,
NA_real_), class = c("POSIXct", "POSIXt"), tzone = ""), TS_EDAT = structure(c(NA_real_,
NA_real_), class = c("POSIXct", "POSIXt"), tzone = ""), SD_SDAT = structure(c(1325545200,
1325545200), class = c("POSIXct", "POSIXt"), tzone = ""), SD_EDAT = structure(c(1357081200,
1357081200), class = c("POSIXct", "POSIXt"), tzone = "")), .Names = c("SUBJECT_Blinded",
"PACKID", "SACDPDAT", "SACRTDAT", "treatment_interval", "TS_SDAT",
"TS_EDAT", "SD_SDAT", "SD_EDAT"), sorted = "SUBJECT_Blinded", class = c("data.table",
"data.frame"), row.names = c(NA, -2L), .internal.selfref = <pointer: 0x0000000002f30788>)