[R] managing dates in POSIXct format at 00

[Stefano Sofia]

Dear R-list users,

this question will seem silly to most of you, but I really got mad trying to find a solution with no success, and therefore I decided to write here.


Suppose I create the following data frame:


mydf <- data.frame(date = c("2007-11-19 00:00:00.000", "2007-11-19 06:00:00.000", "2007-11-19 12:00:00.000", "2007-11-19 18:00:00.000", "2007-11-20 00:00:00.000"), value = rep(10, 5))

mydf$data_POSIX <- as.POSIXct(mydf$date, format = "%Y-%m-%d %H:%M:%S", tz="Etc/GMT-1")

max(mydf$data_POSIX)


gives, obviously,


[1] "2007-11-20 +01"


Now if I export this data frame in a txt file


write.table(mydf, file="mydf.txt", sep = ",", dec=".", row.names=FALSE, col.names = TRUE, quote=FALSE)


the file is stored like


date,value,data_POSIX
2007-11-19 00:00:00.000,10,2007-11-19
2007-11-19 06:00:00.000,10,2007-11-19 06:00:00
2007-11-19 12:00:00.000,10,2007-11-19 12:00:00
2007-11-19 18:00:00.000,10,2007-11-19 18:00:00
2007-11-20 00:00:00.000,10,2007-11-20

Hours, minutes and seconds at 00 are not shown anymore.
When I read back this file into R:

mydf2 <- read.table(file="mydf.txt", header = TRUE, sep=",", dec = ".")

mydf2$data_POSIX <- as.POSIXct(mydf2$data_POSIX, format = "%Y-%m-%d %H:%M:%S", tz="Etc/GMT-1")

I get
                     date value          data_POSIX
1 2007-11-19 00:00:00.000    10                <NA>
2 2007-11-19 06:00:00.000    10 2007-11-19 06:00:00
3 2007-11-19 12:00:00.000    10 2007-11-19 12:00:00
4 2007-11-19 18:00:00.000    10 2007-11-19 18:00:00
5 2007-11-20 00:00:00.000    10                <NA>

and

max(mydf2$data_POSIX)


does not work anymore.

Where is my mistake? Is there a solution?

Thank you for your attention and your help

Stefano





         (oo)
--oOO--( )--OOo--------------------------------------
Stefano Sofia MSc, PhD
Civil Protection Department - Marche Region - Italy
Meteo Section
Snow Section
Via Colle Ameno 5
60126 Torrette di Ancona, Ancona (AN)
Uff: +39 071 806 7743
E-mail: stefano.sofia using regione.marche.it
---Oo---------oO----------------------------------------

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