Às 17:30 de 14/11/2025, Stefano Sofia via R-help escreveu:
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]
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Hello,
Instead of as.POSIXct use strftime. In the second code line below.
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$data_POSIX <- strftime(mydf$date, format = "%Y-%m-%d %H:%M:%S",
tz="Etc/GMT-1")
max(mydf$data_POSIX)
#> [1] "2007-11-20 00:00:00"
write.table(mydf, file="mydf.txt", sep = ",", dec=".", row.names=FALSE,
col.names = TRUE, quote=FALSE)
mydf2 <- read.table(file="mydf.txt", header = TRUE, sep=",", dec = ".")
mydf2
#> date value data_POSIX
#> 1 2007-11-19 00:00:00.000 10 2007-11-19 00:00:00
#> 2 2007-11-19 06:00:00.000 10 2007-11-19 06:00:00
#> 3 2007-11-19 12:00:00.000 10 2007-11-19 12:00:00
#> 4 2007-11-19 18:00:00.000 10 2007-11-19 18:00:00
#> 5 2007-11-20 00:00:00.000 10 2007-11-20 00:00:00
mydf2$data_POSIX <- as.POSIXct(mydf2$data_POSIX, format = "%Y-%m-%d
%H:%M:%S", tz="Etc/GMT-1")
mydf2
#> date value data_POSIX
#> 1 2007-11-19 00:00:00.000 10 2007-11-19 00:00:00
#> 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 2007-11-20 00:00:00
Also, since you are writing to and reading from a CSV file, use
write.csv and read.csv.
write.csv(mydf, file="mydf.txt", row.names=FALSE, quote=FALSE)
mydf2 <- read.csv(file="mydf.txt")
Hope this helps,
Rui Barradas
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PLEASE do read the posting guide https://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
