R does this for convenience when printing values. But it's not always convenient when writing to a file. Instead, you could use strftime to convert to your desired character format before writing:
mydf$data_POSIX <- strftime(mydf$data_POSIX, "%Y-%m-%d %H:%M:%OS3") you can optionally change the 3 to a number between 0 and 6. If you choose 0, it's easier to just use %S instead. On Fri, Nov 14, 2025, 12:30 Stefano Sofia via R-help <[email protected]> wrote: > 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: [email protected] > ---Oo---------oO---------------------------------------- > > ________________________________ > > AVVISO IMPORTANTE: Questo messaggio di posta elettronica può contenere > informazioni confidenziali, pertanto è destinato solo a persone autorizzate > alla ricezione. I messaggi di posta elettronica per i client di Regione > Marche possono contenere informazioni confidenziali e con privilegi legali. > Se non si è il destinatario specificato, non leggere, copiare, inoltrare o > archiviare questo messaggio. Se si è ricevuto questo messaggio per errore, > inoltrarlo al mittente ed eliminarlo completamente dal sistema del proprio > computer. Ai sensi dell'art. Ai sensi dell'art. 2.4 dell'allegato 1 alla > DGR n. 74/2021, si segnala che, in caso di necessità ed urgenza, la > risposta al presente messaggio di posta elettronica può essere visionata da > persone estranee al destinatario. > IMPORTANT NOTICE: This e-mail message is intended to be received only by > persons entitled to receive the confidential information it may contain. > E-mail messages to clients of Regione Marche may contain information that > is confidential and legally privileged. Please do not read, copy, forward, > or store this message unless you are an intended recipient of it. If you > have received this message in error, please forward it to the sender and > delete it completely from your computer system. > > [[alternative HTML version deleted]] > > ______________________________________________ > [email protected] mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > https://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ [email protected] mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide https://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
