R issue with rounding milliseconds

Question

Given the following issue with rounding milliseconds under R. How do I get around it so that the times are correct?

> options(digits.secs=3)
> as.POSI         


        

Answer 1

This is the same problem as Milliseconds puzzle when calling strptime in R.

Your example:

> x <- as.POSIXlt("13:29:56.061", format='%H:%M:%OS', tz='UTC')
> print(as.numeric(x), digits=20)
[1] 1339075796.0610001087

is not representative of the problem. as.numeric(x) converts your POSIXlt object to POSIXct before converting to numeric, so you get different floating-point-precision rounding errors.

That's not how print.POSIXlt (which calls format.POSIXlt) works. format.POSIXlt formats each element of the POSIXlt list construct individually, so you would need to look at:

print(x$sec, digits=20)
[1] 56.060999999999999943

And that number is truncated at the third decimal place, so you see 56.060. You can see this by calling format directly:

> format(x, "%H:%M:%OS6")
[1] "13:29:56.060999"