Parsing ISO8601 in R

Question

Are there any existing implementations in R to parse ISO8601 strings into POSIXt objects? The ISO8601 spec allows date/times to be printed in a variety of (non-overlapping) formats, so one probably needs to do some regular expression magic to detect the format and feed that to strptime.

Doing this properly might actually be quite challenging, however something that detects the most common formats would already be very helpful. I can hardly imagine I am the first one to run into this, but I am having a hard time finding good implementations.

Answer 1

Strictly speaking, you can't. I don't need to know anything about r or cran (or even what they are) to tell you that, because I know ISO 8601 well enough to know that just knowing something is ISO 8601 is not enough to unambiguously know that what is meant by it, especially in the shorter forms.

Find out what profile of ISO 8601 the other party is using. If they don't know what you're talking about, then you will be doing them a favour when you point out what I just said in the paragraph above. As I wrote once elsewhere,

Unfortunately many people think of a particular profile they are familiar with when they hear “ISO 8601”, other people know that using 8601 is a Good Thing but are not familiar with the details of implementation. Hence a spec or requirements document might mention 8601 but not be more explicit than that. In such cases it’s important to seek clarification rather than assume that the format you think of as “ISO 8601” is the correct one to use.

So, tell them "'ISO 8601' is not specific enough, I need to know exactly what you are doing, what your limits on precision are." (And possibly what your policy on dates prior to 1582 and perhaps again prior to 0001 are, your policy on leap-seconds, and a few other things left open but the standard)

Then whatever you're dealing with should be easy enough: Aside from this point of ambiguity, it is a pretty straight-forward standard. It should just be thought of as a standard about defining date formats, more than one that defines a date format.