I have time series data obtained from a data logger that was set to one time zone without daylight savings (NZST or UTC+12:00), and the data spans a few years. Data loggers don't consider DST changes, and are synchronized to local time with/without DST (depending who deployed it).
However, when I get the data into R, I'm unable to properly use as.POSIXct to ignore DST. I'm using R 2.14.0 on a Windows computer with these settings:
> Sys.timezone()
[1] "NZDT"
> Sys.getlocale("LC_TIME")
[1] "English_New Zealand.1252"
Here are three timestamps across the spring DST change, each are spaced 1 hour apart:
> ts_str <- c("28/09/2008 01:00", "28/09/2008 02:00", "28/09/2008 03:00")
> as.POSIXct(ts_str, format="%d/%m/%Y %H:%M", tz="")
[1] "2008-09-28 01:00:00 NZST" NA
[3] "2008-09-28 03:00:00 NZDT"
> as.POSIXct(ts_str, format="%d/%m/%Y %H:%M", tz="UTC")
[1] "2008-09-28 01:00:00 UTC" "2008-09-28 02:00:00 UTC"
[3] "2008-09-28 03:00:00 UTC"
As you can see, the clocks jumped forward at 1:59 to 3:00, so 2:00 is invalid, thus NA. Furthermore, I can use tz="UTC" to get it to ignore DST changes. However, I'd rather keep the correct time zone since I have other data series recorded with DST (NZDT or UTC+13:00) that I'd like to blend in (via merge) for my analysis.
How do I configure the tz parameter on a MS Windows computer? I've tried many things, such as "NZST", "New Zealand Standard Time", "UTC+12:00", "+1200", etc., but no luck. Or do I modify some other setting?
You can use tz="Etc/GMT+12":
as.POSIXct(ts_str, format="%d/%m/%Y %H:%M", tz="Etc/GMT+12")
[1] "2008-09-28 01:00:00 GMT+12" "2008-09-28 02:00:00 GMT+12"
[3] "2008-09-28 03:00:00 GMT+12"
For a full list of available timezones use,
dir(file.path(R.home("share"),"zoneinfo"), recursive=TRUE)
There are a couple of of .tab files in there which aren't timezones but hold some information, but my regex-fu isn't good enough to be able to exclude them with the pattern argument to dir.
If just add 12*60*60 to that UTC derived vector, you will have local "standard" time.
Related
I would like to use R for time series analysis. I want to make a time-series model and use functions from the packages timeDate and forecast.
I have intraday data in the CET time zone (15 minutes data, 4 data points per hour). On March 31st daylight savings time is implemented and I am missing 4 data points of the 96 that I usually have. On October 28th I have 4 data points too many as time is switched back.
For my time series model I always need 96 data points, as otherwise the intraday seasonality gets messed up.
Do you have any experiences with this? Do you know an R function or a package that would be of help to automat such data handling - something elegant?
Thank you!
I had a similar problem with hydrological data from a sensor. My timestamps were in UTC+1 (CET) and did not switch to daylight saving time (UTC+2, CEST). As I didn't want my data to be one hour off (which would be the case if UTC were used) I took the %z conversion specification of strptime. In ?strptime you'll find:
%z Signed offset in hours and minutes from UTC, so -0800 is 8 hours
behind UTC.
For example: In 2012, the switch from Standard Time to DST occured on 2012-03-25, so there is no 02:00 on this day. If you try to convert "2012-03-25 02:00:00" to a POSIXct-Object,
> as.POSIXct("2012-03-25 02:00:00", tz="Europe/Vienna")
[1] "2012-03-25 CET"
you don't get an error or a warning, you just get date without the time (this behavior is documented).
Using format = "%z" gives the desired result:
> as.POSIXct("2012-03-25 02:00:00 +0100", format="%F %T %z", tz="Europe/Vienna")
[1] "2012-03-25 03:00:00 CEST"
In order to facilitate this import, I wrote a small function with appropriate defaults values:
as.POSIXct.no.dst <- function (x, tz = "", format="%Y-%m-%d %H:%M", offset="+0100", ...)
{
x <- paste(x, offset)
format <- paste(format, "%z")
as.POSIXct(x, tz, format=format, ...)
}
> as.POSIXct.no.dst(c("2012-03-25 00:00", "2012-03-25 01:00", "2012-03-25 02:00", "2012-03-25 03:00"))
[1] "2012-03-25 00:00:00 CET" "2012-03-25 01:00:00 CET" "2012-03-25 03:00:00 CEST"
[4] "2012-03-25 04:00:00 CEST"
If you don't want daylight saving time, convert to a timezone that doesn't have it (e.g. GMT, UTC).
times <- .POSIXct(times, tz="GMT")
Here is getting the daylight savings time offset -
e.g. Central Daylight Savings time
> Sys.time()
"2015-08-20 07:10:38 CDT" # I am at America/Chicago daylight time
> as.POSIXct(as.character(Sys.time()), tz="America/Chicago")
"2015-08-20 07:13:12 CDT"
> as.POSIXct(as.character(Sys.time()), tz="UTC") - as.POSIXct(as.character(Sys.time()), tz="America/Chicago")
Time difference of -5 hours
> as.integer(as.POSIXct(as.character(Sys.time()), tz="UTC") - as.POSIXct(as.character(Sys.time()), tz="America/Chicago"))
-5
Some inspiration was from
Converting time zones in R: tips, tricks and pitfalls
I have dates and times stored in two columns. The first has the date as "20180831." The time is stored as the number of seconds from midnight; 3am would be stored as 10,800.
I need a combined date time column and am having a hard time with something that should be simple.
I can get the dates in no problem but lubridate "hms" interprets the time field as a period, not a 'time' per se.
I tried converting the date to posix.ct format and then using that as the origin for the time field but posix.ct does not set the time for midnight, instead it sets it for either 1800 or 1900 hours depending on the date. I need it set to midnight for all rows, I don't want any daylight savings time adjustment.
Here's the code:
First I made a function because there are several date and time fields I have to do this for.
mkdate<-function(x){
a<-as.Date(as.character(x),format='%Y%m%d')
a<-as.POSIXct(a)
return(a)
}
df$date<-mkdate(df$date) #applies date making function to date field
df$datetime<-as.POSIXct(df$time,origin=df$date)
I'm sure this has to do with time zones. I'm in Central time zone and I have experimented with adding the "tz" specification into these commands in both the mkdate function and in the time code creating "datetime" column.
I've tried:
tz="America/Chicago"
tz="CST"
tz="UTC"
Help would be much appreciated!
Edited with example:
x<-c(20180831,20180710,20160511,20170105,20180101) #these are dates.
as.POSIXct(as.Date(as.character(x),format="%Y%m%d"))
Above code converts dates to seconds from the Jan 1 1970. I could convert this to numeric and add my 'seconds' value to this field BUT it is not correct. This is what I see instead as the output:
[1] "2018-08-30 19:00:00 CDT" "2018-07-09 19:00:00 CDT" "2016-05-10 19:00:00 CDT" "2017-01-04 18:00:00 CST" "2017-12-31 18:00:00 CST"
Look at the first date - it should be 8/31 but instead it is 8/30. Somewhere in there there is a timezone adjustment taking place. It's moving the clock back 5 or 6 hours because I am on central time. The first entry should be 2018-08-31 00:00:00. I would then convert it to numeric and add the seconds field on and convert back to POSIXct format. I've tried including tz specification all over the place with no luck.
Sys.getlocale("LC_TIME")
returns "English_United States.1252"
I believe the following does what you want.
My locale is the following, so the results are different from yours.
Sys.getlocale("LC_TIME")
#[1] "Portuguese_Portugal.1252"
The difference will be due to the daylight savings time, the summer hour.
As for your problem, all you have to do is to remeber that the objects of class "POSIXct are coded as the number of seconds since an origin, and that origin is usually the midnight of 1970-01-01. So you have to add your seconds since midnight to the seconds of as.Date.
x <- "20180831"
xd <- mkdate(x)
y <- 10800
as.POSIXct(as.integer(xd) + y, origin = "1970-01-01")
#[1] "2018-08-31 04:00:00 BST"
as.POSIXct(as.integer(xd) + y, origin = "1970-01-01", tz = "America/Chicago")
#[1] "2018-08-30 22:00:00 CDT"
There are very many ways to do this:
mktime = function(a, b)modifyList(strptime(a, '%Y%m%d'), list(sec = as.numeric(gsub(',', '', b))))
mktime("20180831",'10,800')
[1] "2018-08-31 03:00:00 PDT"
mktime('20180301','10800')
[1] "2018-03-01 03:00:00 PST"
mktime('20180321','10800')
[1] "2018-03-21 03:00:00 PDT"
Looking at the above code, it does not adjust for the daylight saving time. Irrespective of the date, the seconds still show that it Is 3 AM, including the dates when ST-->DT. This will also take into consideration, your LOCAL timezone.
I am trying to convert UTC time to local standard time. I have found many functions which convert to Local Daylight Time, but I was not successful in getting the standard time. Right now, I have the following code which converts to local daylight time at my specific timezone:
pb.date <- as.POSIXct(date,tz="UTC")
format(pb.date, tz="timeZone",usetz=TRUE)
I would appreciate any help.
First, POSIXct date-times are always UCT internally. The print.POSIXt and format.POSIXt methods will appropriately make the TZ shift on output from their internal representations:
pb.date <- as.POSIXct(Sys.Date())
Sys.Date()
#[1] "2015-07-09"
So that was midnight of the current date in Greenwich:
format(pb.date, tz="America/Los_Angeles",usetz=TRUE)
#[1] "2015-07-08 17:00:00 PDT"
When it's midnight in Greenwich, it's 5PM Daylight Time in the previous day on the Left Coast of the US. You need to use the correct character values for your TZ (and your OS) both of which at the moment are unspecified.
The US Pacific timezone is 8 hours behind GMT (in winter months) so you can use a timezone that is Standard/Daylight-agnostic:
> format(pb.date,usetz=TRUE, tz="Etc/GMT+8")
[1] "2015-07-08 16:00:00 GMT+8"
(Notice the reversal of + with "behind" and - with "ahead".)
I know this question has an accepted answer, but in case anyone comes along and this can help. I needed a function to convert UTC times to MTN time (Server is in UTC, we operate in MTN).
Not sure why, but needed to force it to UTC/GMT first and the convert it to MTN. However it does work
mtn_ts = function(utcTime){
library(lubridate)
toTz = "us/mountain"
utcTime = force_tz(utcTime,tzone= 'GMT')
dt = as.POSIXct(format(utcTime,tz = toTz,origin ='GMT', usetz=TRUE))
dt = force_tz(dt,tzone= toTz)
return(dt)
}
mtn_ts(as.POSIXct("2021-09-27 14:48:51.000000000"))
I am using the weatherData package, specifically, its getDetailedWeather function. It returns a data frame, one of the component of the data frame is Time, of class POSIXct. My problem is that all the Time comes set to the local timezone of the machine I am using. I am pretty sure that this is incorrect, that the data reflects the local time, and the only thing the API does is add the timezone to the data, without changing it. Am I correct? How can I tell the API to stop using my timezone as default?
E.g.:
library(weatherData)
dat <- getDetailedWeather("NRT", "2014-04-29")
dat$Time
# [1] "2014-04-29 00:00:00 EST" ## local timezone, not of the weather station
Looking at the results of the example in ?getDetailedWeather:
library(weatherData)
dat <- getDetailedWeather("NRT", "2014-04-29")
dat$Time
# [1] "2014-04-29 00:00:00 EST" "2014-04-29 00:30:00 EST" "2014-04-29 01:00:00 EST" etc
The returned times seem to be 'correct', in that it goes from 00:00 to 23:30. The timezone for the data is not that of the weather station though, but rather of the host computer system. You may be best off just changing this output data once you have it, as R will always present date/time POSIXct objects in the local timezone by default, e.g.:
as.POSIXct(as.character(dat$Time),tz="UTC")
# [1] "2014-04-29 00:00:00 UTC" "2014-04-29 00:30:00 UTC" "2014-04-29 01:00:00 UTC" etc
The above changes the timezone to a new timezone (in this case "UTC", but you could use one appropriate for the weather station location) without affecting the time of day data. See here: Valid time zones in lubridate for identifying local timezone codes.
This code works:
ISOdatetime(2011,4,7,12,0,0, tz = "EST")
This code does not:
ISOdatetime(2011,4,7,12,0,0, tz = "CST")
I want the central time zone, with no adjustment for daylight savings. What am I doing wrong? Where can I find a table of timezones recognized by R?
edit: Thanks for the info Josh, but ISOdatetime(2011,3,13,2,0,0, tz = "America/Chicago") yields NA, and is unfortunately a value in my dataset. Any ideas how to deal with this? It seems like my dataset is on Chicago time, but does not observe daylight savings time.
See ?timezone and the file, R_HOME/share/zoneinfo/zone.tab.
There's no such thing as "the central time zone, with no adjustment for daylight savings". The US central time zone has DST rules and they have changed over the years. You could always read in your dates as GMT, add 6 hours, then convert to CST6CDT.
> .POSIXct(ISOdatetime(2011,3,13,2,0,0, tz="GMT")+3600*6, tz="CST6CDT")
[1] "2011-03-13 03:00:00 CDT"
> .POSIXct(ISOdatetime(2011,3,13,2,0,0, tz="GMT")+3600*6, tz="America/Chicago")
[1] "2011-03-13 03:00:00 CDT"