fwrite doesn't save dates

[skanskan]

Hello.

I have a dataset. I can choose to load it on R from a Stata file or from a SPSS file.
In both cases it's loaded properly with the haven package.
The dates are recognized properly.

But when I save it to disk with data.table's fwrite.
fwrite(ppp, "ppp.csv", sep=",", col.names = TRUE)
I have a problem, the dates dissapear and are converted to numbers with no sense.

For example the date 1967-08-06 now is -879

I've also tried playing with fwrite options, such as quote=FALSE, with no success.

I've uploaded a small sample of the files, the spss, the stata and the saved csv.

library(haven)
library(data.table)
ppp <- read_sav("pspss.sav") # choose one of these two.
ppp <- read_dta("pstata.dta")  # choose one of these two.
fwrite(ppp, "ppp.csv",  sep=",", col.names = TRUE) 

http://www73.zippyshare.com/v/OwzwbyQq/file.html

How can I solve it?

Regards

[arunsrinivasan]

Duplicate of #1664. It's not yet implemented.

What you're seeing is the internal representation. By setting class attribute to Date, you should be able to see the date.

[skanskan]

When should I set the class attribute to Date? When fwriting or when reading back? And how?

When I read back the csv file with fread the 1967-08-06 date still appears as -879 .
Regards

[arunsrinivasan]

After reading it back. attr(dt$col, 'class') = "Date" or class(dt$col) = "Date" or setattr(dt$col, 'class', "Date").

[skanskan]

OK, thank you.
Any easy way to do it easily?. The real file has 1200 variables, many of them are dates.
I mean some way to save the original column classes and change the new...

[skanskan]

Since it seems there is no simple solution I'm trying to store column classes and change them back again.

I've taken the original dataset ppp,

areDates <- (sapply(ppp, class) == "Date")

I save it on an file and I can read it next time.

ppp <- fread("ppp.csv", encoding="UTF-8")

And now I change the classes of the newly read dataset back to the original one.

ppp[,names(ppp)[areDates] := lapply(.SD,as.Date) , .SDcols = areDates ]

The problem is that it works with this toy example but with the real big example I get the error:

Error in as.Date.numeric(X[[i]], ...) : 'origin' must be supplied

I've also tried with
lapply(.SD,function(xx) class(xx) <- "Date")
but it fills the variables with NA

[jangorecki]

@skanskan I would try lapply(., setattr, "class", "Date"), but just guessing. Changing class of elements in a list fits more on Stackoverflow. Date class is just a numeric having own methods, you "convert" it just by add or drop class attribute (unless you use origin attribute). There is separate issue which discuss that fact and its potential for IO performance (fread-fwrite) when writing Date in string representation will be already implemented, see #1656