R crashes while using data.table - r

Question

sac[,treatment_days := as.character(seq(from = SACDPDAT, to = SACRTDAT, by = "1 day")), by = PACKID] I have data named sac with dput(sac[1:2,]) as follows:
structure(list(SUBJECT_Blinded = c(1201001, 1101001), LINE = c(8,
4), MODULE = c("SAC", "SAC"), CENTRE_Blinded = c(1201, 1201),
STUDYPER = c(7, 4), PACKID = c(10096, 10595), SACDPDAT = structure(c(1335304800,
1325545200), class = c("POSIXct", "POSIXt"), tzone = ""),
SACDP1 = c(35, 35), C_SACDP = c(NA_character_, NA_character_
), SACRTDAT = structure(c(1340316000, 1327964400), class = c("POSIXct",
"POSIXt"), tzone = ""), SACRT1 = c(0, 9), C_SACRT = c(NA_character_,
NA_character_)), .Names = c("SUBJECT_Blinded", "LINE", "MODULE",
"CENTRE_Blinded", "STUDYPER", "PACKID", "SACDPDAT", "SACDP1",
"C_SACDP", "SACRTDAT", "SACRT1", "C_SACRT"), sorted = c("SUBJECT_Blinded",
"PACKID"), class = c("data.table", "data.frame"), row.names = c(NA,
-2L))
When I running the code:
sac[,treatment_days := list(format(seq(from = SACDPDAT, to = SACRTDAT, by = "1 day"),"%Y-%m-%d")), by = PACKID]
RStudio crushes and returns info:
Problem signature:
Problem Event Name: APPCRASH
Application Name: rsession.exe
Application Version: 0.98.501.0
Application Timestamp: 52e8371d
Fault Module Name: R.dll
Fault Module Version: 3.3.65126.0
Fault Module Timestamp: 53185fd3
Exception Code: c0000005
Exception Offset: 0000000000028c36
OS Version: 6.1.7601.2.1.0.256.48
Locale ID: 1045
Additional Information 1: 4fc0
Additional Information 2: 4fc0e6e5b53a870c89fb6e37a38d7e6b
Additional Information 3: 9d6e
Additional Information 4: 9d6e8f79167930945e5a5d06afac680e
It's the same with pure R. Any ideas how to do it another way?

Answer 1

There's a couple of problems with your new code:
"1 day" is incorrect, if you run seq on a date object, the number you pass to by will be interpreted as days, so:
seq(from = SACDPDAT, to = SACRTDAT, by = 1)
You also cannot create a new column from this sequence, because there can only be one value for each row. Instead, you can generate the sequence of days by PACKID, and then join this onto the old data.table
So try:
setkey(sac, PACKID)
sac <- sac[sac[,seq(from = SACDPDAT, to = SACRTDAT, by = 1), by=PACKID]]