[R] write.table read.table with Dates

[JeeBee]

I've found several similar issues with write.table/read.table
with Dates on this list, but trying to follow this advice I still
get an error.

First, I read in data from several files, constructing several date/time
columns using ISOdatetime

> str(Tall$Begin)
'POSIXct', format: chr [1:40114] "2005-10-02 00:00:00" "2005-10-02
00:00:00" ...
> length(Tall$Begin)
[1] 40114
> class(Tall$Begin)
[1] "POSIXt"  "POSIXct"

This looks good (time is not always 00:00:00 ...)
This data came from several files, now I want to store the result I have
in data.frame Tall and be able to retrieve this quickly some other time.

This is what I do:
write.table(Tall, file="somefile.csv", sep=",", qmethod="double",
row.names=FALSE)

Later, I do this to read the file again:
fieldnames=c("Begin","test-a","test-b","Eind")
T=read.table(file = "somefile.csv", col.names = fieldnames,
  header = TRUE, sep = ",", quote="\"", fill=FALSE)

I understand T$Begin now is a factor. I tried to simply convert it
again using (as I read on this mailinglist ...):
Q = strptime(as.character(T$Begin),format="%Y-%m-%d %H:%M:%S")

Q is looking good, though its length I don't understand .. is it a list or
something? It seems there are 40114 values in there somewhere...

> class(Q)
[1] "POSIXt"  "POSIXlt"
> length(Q)
[1] 9
> str(Q)
'POSIXlt', format: chr [1:40114] "2005-10-02 00:00:00" "2005-10-02 00:00:00" ...

T$Begin = Q ### yields this error
Error in "$<-.data.frame"(`*tmp*`, "Begin", value = list(sec = c(0, 0,  :
        replacement has 9 rows, data has 40114

Could somebody explain me how to convert the date column?
Or perhaps there is an easier way?

Thanks in advance for your time.