I'm trying to calculate a date - 1 (basically the day before the date) in R and when it converts it to a POSIXct it seems to subtract another date?
The column is of type POSIXct:
class(df$Date)
[1] "POSIXct" "POSIXt"
Here's the initial value:
> df[12,"Date"]
[1] "2016-03-09 EST"
If I just do as.Date and subtract one it works fine:
as.Date(df[12,"Date"]-1, tz="EST")
[1] "2016-03-08"
But I'm saving it back to the same column so it converts is back to as.POSIXct automatically (I think). And then I end up with March 7 in that column. And 7 pm. If I type it out here I get this:
as.POSIXct(as.Date(df[12,"Date"]-1, tz="EST"))
[1] "2016-03-07 19:00:00 EST"
I've tried using America/New York for the tz. I've tried the as.Date around just the df[12,"Date"] or around the whole thing including the -1... I have no clue what to do!
Thanks!
Use as.difftime to take away amounts specified in units of time. It will work consistently regardless of your data being in Date or POSIXct formats. E.g.:
This fails as you described:
x <- as.POSIXct(c("2016-03-09","2016-03-10"), tz="US/Eastern")
#[1] "2016-03-09 EST" "2016-03-10 EST"
x[1] <- as.Date(x[1]-1, tz="US/Eastern")
#[1] "2016-03-07 19:00:00 EST" "2016-03-10 00:00:00 EST"
This works:
x <- as.POSIXct(c("2016-03-09","2016-03-10"), tz="US/Eastern")
#[1] "2016-03-09 EST" "2016-03-10 EST"
x[1] <- x[1] - as.difftime(1, units="days")
#[1] "2016-03-08 EST" "2016-03-10 EST"
If you don't want to do what Frank mentioned in the comments,
You should consider using strptime instead of as.POSIXct
To ensure it returns in a POSIXct format use:
strptime(df[12,"Date"]-1,tz="EST",format="%Y-%m-%d")
Related
I have a date that I convert to a numeric value and want to convert back to a date afterwards.
Converting date to numeric:
date1 = as.POSIXct('2017-12-30 15:00:00')
date1_num = as.numeric(date1)
# 1514646000
Reconverting numeric to date:
as.Date(date1_num, origin = '1/1/1970')
# "4146960-12-12"
What am I missing with the reconversion? I'd expect the last command to return my original date1.
As the numeric vector is created from an object with time component, reconversion can also be in the same way i.e. first to POSIXct and then wrap with as.Date
as.Date(as.POSIXct(date1_num, origin = '1970-01-01'))
#[1] "2017-12-30"
You could use anytime() and anydate() from the anytime package:
R> pt <- anytime("2017-12-30 15:00:00")
R> pt
[1] "2017-12-30 15:00:00 CST"
R>
R> anydate(pt)
[1] "2017-12-30"
R>
R> as.numeric(pt)
[1] 1514667600
R>
R> anydate(as.numeric(pt))
[1] "2017-12-30"
R>
POSIXct counts the number of seconds since the Unix Epoch, while Date counts the number of days. So you can recover the date by dividing by (60*60*24) (let's ignore leap seconds), or convert back to POSIXct instead.
as.Date(as.numeric(date1)/(60*60*24), origin="1970-01-01")
[1] "2017-12-30"
as.POSIXct(as.numeric(date1),origin="1970-01-01")
[1] "2017-12-30 15:00:00 GMT"
Using lubridate :
lubridate::as_datetime(1514646000)
[1] "2017-12-30 15:00:00 UTC"
This question already has answers here:
Convert date-time string to class Date
(4 answers)
Closed 3 years ago.
I have date&time stamp as a character variable
"2018-12-13 11:00:01 EST" "2018-10-23 22:00:01 EDT" "2018-11-03 14:15:00 EDT" "2018-10-04 19:30:00 EDT" "2018-11-10 17:15:31 EST" "2018-10-05 13:30:00 EDT"
How can I strip the time from this character vector?
PS: Can someone please help. I have tried using strptime but I am getting NA values as a result
It's a bit unclear whether you want the date or time but if you want the date then as.Date ignores any junk after the date so:
x <- c("2018-12-13 11:00:01 EST", "2018-10-23 22:00:01 EDT")
as.Date(x)
## [1] "2018-12-13" "2018-10-23"
would be sufficient to get a Date vector from the input vector x. No packages are used.
If you want the time then:
read.table(text = x, as.is = TRUE)[[2]]
## [1] "11:00:01" "22:00:01"
If you want a data frame with each part in a separate column then:
read.table(text = x, as.is = TRUE, col.names = c("date", "time", "tz"))
## date time tz
## 1 2018-12-13 11:00:01 EST
## 2 2018-10-23 22:00:01 EDT
I think the OP wants to extract the time from date-time variable (going by the title of the question).
x <- "2018-12-13 11:00:01 EST"
as.character(strptime(x, "%Y-%m-%d %H:%M:%S"), "%H:%M:%S")
[1] "11:00:01"
Another option:
library(lubridate)
format(ymd_hms(x, tz = "EST"), "%H:%M:%S")
[1] "11:00:01"
The package lubridate makes everything like this easy:
library(lubridate)
x <- "2018-12-13 11:00:01 EST"
as_date(ymd_hms(x))
You can use the as.Date function and specify the format
> as.Date("2018-12-13 11:00:01 EST", format="%Y-%m-%d")
[1] "2018-12-13"
If all values are in a vector:
x = c("2018-12-13 11:00:01 EST", "2018-10-23 22:00:01 EDT",
"2018-11-03 14:15:00 EDT", "2018-10-04 19:30:00 EDT",
"2018-11-10 17:15:31 EST", "2018-10-05 13:30:00 EDT")
> as.Date(x, format="%Y-%m-%d")
[1] "2018-12-13" "2018-10-23" "2018-11-03" "2018-10-04" "2018-11-10"
[6] "2018-10-05"
I am trying to get the last minute of yesterday using Sys.Date() in Posix time.
force_tz(as.POSIXlt(Sys.Date()-1), tz = 'America/New_York') + 86399
# [1] "2018-01-12 23:59:59 EST"
CORRECT
force_tz(as.POSIXct(Sys.Date()-1), tz = 'America/New_York') + 86399
# [1] "2018-01-12 15:59:59 EST"
INCORRECT
Sys.Date()
# [1] "2018-01-13"
Why does as.Posixct and as.Posixlt return two different values using Sys.Date() and why is the difference 8 hours even after applying force_tz from lubridate ?
As ever, debugonce is your friend. Running debugonce(force_tz), you can see that the difference in output comes from when force_tz hits the branches checking first is.POSIXct(time) (in which case the default tzone = "" is applied); in the POSIXlt case, the default branch is hit, where as.POSIXct is applied to time and tz(time) (which comes out as UTC for a POSIXlt object) is used as the time zone.
This comes down to something subtle happening; from ?as.POSIXlt.Date:
Dates without times are treated as being at midnight UTC.
Hence
tz(as.POSIXlt(Sys.Date()-1))
# [1] "UTC"
But
tz(as.POSIXct(Sys.Date()-1))
# [1] ""
What's peculiar is this can't be overridden -- as.POSIXlt.Date doesn't accept a tz argument:
formals(as.POSIXlt.Date)
# $x
# $...
If you want to use POSIXct, how about the following?
force_tz(as.POSIXct(sprintf('%s 00:00:00', Sys.Date())), 'America/New_York') - 1L
# [1] "2018-01-12 23:59:59 EST"
Here's a weird artifact. I'm converting tens of thousands of character vectors into a datetime class, like so:
alles$DateTime=as.POSIXct(alles$roughdate, tz="EST",format="%Y%m%d.%H%M%S.%OS")
Pretty straight forward. The character string (alles$roughdate) is in the format YYYYMMDD.HHMMSS.ss with the .ss being milliseconds. The above code works, as would be expected. However, if the milliseconds equal .61, it returns an NA instead of a date time value.
This isn't too bad, but when dealing with tens of thousands cells, a few hundred are always returned as NA. Milliseconds always .61, doesn't matter what the rest of the date is. I do need those dates.
I've tried isolating those files and then merging the two data frames together again, but that doesn't seem to work. All of my dates are suddenly NA.
Any thoughts?
Example
vec <- c("20150101.010101.60", "20150101.010101.61", "20150101.010101.62")
as.POSIXlt(vec, tz="EST", format="%Y%m%d.%H%M%S.%OS")
#[1] "2015-01-01 01:01:60 EST" NA "2015-01-01 01:01:01 EST"
If you change the format for the time part to be %H%M%OS instead of %H%M%S.%OS, it seems to parse correctly. You may have to adjust your options so see this:
as.POSIXlt(vec, tz = "EST", format = "%Y%m%d.%H%M%OS")
#[1] "2015-01-01 01:01:01 EST" "2015-01-01 01:01:01 EST"
#[3] "2015-01-01 01:01:01 EST"
options(digits.secs = 2)
as.POSIXlt(vec, tz = "EST", format = "%Y%m%d.%H%M%OS")
# [1] "2015-01-01 01:01:01.60 EST" "2015-01-01 01:01:01.61 EST"
# [3] "2015-01-01 01:01:01.62 EST"
My question comes from this question. The question had the following character string.
x <- "2007-02-01 00:00:00"
y <- "02/01/2007 00:06:10"
If you try to convert this string to date-class object, something funny happens.
This is a sample from #nrusell's answer.
as.POSIXct(x,tz=Sys.timezone())
[1] "2007-02-01 EST"
as.POSIXct(y,format="%m/%d/%Y %H:%M:%S",tz=Sys.timezone())
[1] "2007-02-01 00:06:10 EST"
As you see, 00:00:00 disappears from the first example. #Richard Scriven left the following example in our discussion using lubridate.
dt <- as.POSIXct("2007-02-01 00:00:00")
hour(dt) <- hour(dt)+1
dt
[1] "2007-02-01 01:00:00 EST"
hour(dt) <- hour(dt)-1
dt
[1] "2007-02-01 EST"
Once again, 00:00:00 disappears. Why does R avoid keeping 00:00:00 in date-class object after conversion? How can we keep 00:00:00?
It is just the print that remove the precision if the time part of a date is a midnight. This is literlay explained in ??strftime help, specially the format parameter:
A character string. The default is "%Y-%m-%d %H:%M:%S" if any
component has a time component which is not midnight, and "%Y-%m-%d"
otherwise
One idea is to redefine the S3 method print for POSIXct object:
print.POSIXct <- function(x,...)print(format(x,"%Y-%m-%d %H:%M:%S"))
Now for your example if your print your x date(with midnight part) you get:
x <- "2007-02-01 00:00:00"
x <- as.POSIXct(x,tz=Sys.timezone())
x
[1] "2007-02-01 00:00:00"