How to Convert Unix Timestamp (Milliseconds) and Timezone in R

How to convert unix timestamp (milliseconds) and timezone in R?

It looks like the timezone column is the timezone offset, in milliseconds. I assume that means the timezone column will adjust for daylight saving time manually

So you should add the time and timezone columns before converting to POSIXct. You should also set the tz to "UTC" so no DST adjustments will be made to your POSIXct object.

R> time <- 1433848856453
R> timezone <- 10800000
R> options(digits.secs=3)
R> .POSIXct((time+timezone)/1000, tz="UTC")
[1] "2015-06-09 14:20:56.453 UTC"

Convert UNIX epoch to Date object

Go via POSIXct and you want to set a TZ there -- here you see my (Chicago) default:

R> val <- 1352068320
R> as.POSIXct(val, origin="1970-01-01")
[1] "2012-11-04 22:32:00 CST"
R> as.Date(as.POSIXct(val, origin="1970-01-01"))
[1] "2012-11-05" 
R> 

Edit: A few years later, we can now use the anytime package:

R> library(anytime)
R> anytime(1352068320)
[1] "2012-11-04 16:32:00 CST"
R> anydate(1352068320)
[1] "2012-11-04"
R> 

Note how all this works without any format or origin arguments.

Convert data frame with epoch timestamps to time-series with milliseconds in R

Your timestamps are in milliseconds. You need to convert them to seconds to be able to use them with as.POSIXct. And there's no point in calling strptime on a POSIXct vector.

Also, it's good practice to explicitly set the timezone, rather than leave it set to "".

df$datetime <- as.POSIXct(df$timestamp/1000, origin="1970-01-01", tz="UTC")
options(digits.secs=6)
df
#     timestamp session                datetime
# 1 1.42832e+12       A 2015-04-06 11:29:30.510
# 2 1.42832e+12       A 2015-04-06 11:29:57.217
# 3 1.42832e+12       B 2015-04-06 11:29:58.181
# 4 1.42832e+12       A 2015-04-06 11:30:03.326
# 5 1.42832e+12       A 2015-04-06 11:30:08.477

I'm not sure why you aren't seeing millisecond resolution...

R - converting a timestamp to a local time and date

You get the same output in all 3 cases because 1) and 3) are same (UTC and GMT) whereas 2) (DST) is not a valid tz value.

If you don't mention the timezone value it should by default give you time in your local time zone.

as.POSIXct(as.numeric('1594598065352')/1000, origin="1970-01-01")

---

Alternatively, you can run OlsonNames() in your console to get list of valid timezones in R. 'Etc/GMT-2' seems to be the one for you.

as.POSIXct(as.numeric('1594598065352')/1000,origin="1970-01-01", tz = 'Etc/GMT-2')
#[1] "2020-07-13 01:54:25 +02"

how to extract year, tz-convert and get millisecond part from a nanotime timestamp?

I do all of this with data.table because it is known that data.table supports the underlying bit64 package and integer64 representation that is needed here. Other containers do not.

Code

library(nanotime)
library(data.table)

DT <- data.table(ts =  c(nanotime('2011-12-05 08:30:00.000',format ="%Y-%m-%d %H:%M:%E9S",  tz ="GMT"),
                         nanotime('2011-12-05 08:30:00.700',format ="%Y-%m-%d %H:%M:%E9S",  tz ="GMT"),
                          nanotime('2011-12-05 08:30:00.825',format ="%Y-%m-%d %H:%M:%E9S",  tz ="GMT")))
DT[, pt := as.POSIXct(ts)]
DT[, millis := as.numeric(pt - trunc(pt)) * 1e3]

Result

R> DT
                                    ts                      pt millis
1: 2011-12-05T08:30:00.000000000+00:00 2011-12-05 02:30:00.000      0
2: 2011-12-05T08:30:00.700000000+00:00 2011-12-05 02:30:00.700    700
3: 2011-12-05T08:30:00.825000000+00:00 2011-12-05 02:30:00.825    825
R> 

Timezone shifts are a different (and misunderstood) topic. You can do it to POSIXct.

Note that all you have done here / asked for here was the millisecond resolution. So far no need was demonstrated for nanotime. But what I showed you can work on nanoseconds -- I use it every day from data.table.

---

Related Topics