[R] aggregating dates

[Paul Sorenson]

I have a frame which contains 3 columns:

"date" "defectnum" "state"

And I want to get the most recent state change for a given defect number.  date is POSIXct.

I have tried:
	aggregate(ev$date, by=list(ev$defectnum), max)

Which appears to be working except that the dates seem to come back as integers (presumably the internal representation of POSIXct).

When I execute max(ev$date) the result remains POSIXct.

I have been dredging through the help among DateTimeClasses and haven't found a function that converts these integers to some kind of date class.  Or a method for using aggregate which doesn't perform the conversion in the first place.

Any clues?