Support partial dates

[tidyverse]

Support partial dates

[garrettgman]

What would you want to be able to do with them? I think that might determine how we would implement this.

[vsbuffalo]

I support this. I ran into this issue yesterday and it was incredibly frustrating. At the very least, lubridate should have graceful error messages. Consider:

> parse_date_time("April-2012", "%B-%Y")
Error in formats[[1]] : subscript out of bounds

Python's datetime library:

>>> from datetime import datetime
>>> datetime.strptime("April-2012", "%B-%Y")
datetime.datetime(2012, 4, 1, 0, 0)

Using the first date of a month is a good default behavior until NA date components can be added.

[vspinu]

First, this is a bug, and the helpful message were supposed to happen later. Second, it actually occurs because the underlying C implementation of stprptime doesn't parse partial dates of these sort. This is expectedly mentioned in the documentation of parse_date_time.

[vspinu]

New parser supports partial dates for numeric formats:

> parse_date_time(c("2/10","2/11"), "my")
[1] "2010-02-01 UTC" "2011-02-01 UTC"

Alphanumeric formats will unlikely be ever supported as it would require managing locales explicitly. Users can simply append 01 in front of truncated dates to overcome the issue.