R Change date YY-MM-DD hh:mm to time since origin (Days.Seconds)

Question

I have a date input like this (currently as character class):

input=c("2013-05-08 11:20:10", "2013-05-08 11:21:09")

And want to have an output like this:

output=c(127.472338, 127.473032)

Which is the time since origin (2013-01-01 00:00:00) in days and seconds.

Previously, I used data in the output format and reconverted it to the input format using:

temp=as.POSIXlt(output*24*3600,origin='2013-01-01 00:00:00', tz="Etc/GMT+0")

How can I rewrite this so that I get the desired output? Thanks in advance.

Perhaps `as.numeric(difftime(as.POSIXlt(input), as.POSIXlt('2013-01-01 00:00:00')))` — akrun, Sep 02 '15 at 11:56

score 4 · Answer 1 · answered Sep 02 '15 at 11:57

4

Use difftime (or -):

> difftime(as.POSIXct(input), as.POSIXct("2013-01-01"))
Time differences in days
[1] 127.4307 127.4314
> as.POSIXct(input) - as.POSIXct("2013-01-01")
Time differences in days
[1] 127.4307 127.4314

answered Sep 02 '15 at 11:57

Joshua Ulrich

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You don't even need the `as.POSIXct` part: `difftime(input, "2013-01-01",units="days")` works just fine. – nicola Sep 02 '15 at 12:45
@nicola: while true, I'm not a particular fan of implicit conversion from character to Date/POSIXt. – Joshua Ulrich Sep 02 '15 at 13:26
And you are totally right. I just wanted to stress how easy can be to obtain some results in R. – nicola Sep 02 '15 at 13:28
@nicola: yes... too easy. :) – Joshua Ulrich Sep 02 '15 at 13:58
Thank you both very much :) – Anne Sep 02 '15 at 16:04
I just noticed that the time I get with this solution is off by one hour. However, if I use the following, I get the right results: `temp2=difftime(input, "2013-01-01 00:00:00", tz="Etc/GMT+0")` – Anne Sep 03 '15 at 08:26

R Change date YY-MM-DD hh:mm to time since origin (Days.Seconds)

1 Answers1