Help interpreting/converting odd date format

Question

I have data pulled from a database and stored in Stata .dta files. But when I read it into R using the foreign package, I get a date format unlike any I've seen. All of the other dates are "%m/%d/%Y" and import correctly.

I have searched the database's documentation, but there's no explanation for the odd date format for "DealActiveDate". The "facilitystartdate" date should be close to the "DealActiveDate", but not necessarily the same. Here are a few rows of these two columns.

facilitystartdate DealActiveDate
1         09/12/1987   874022400000
2         09/12/1987   874022400000
3         09/12/1987   874022400000
4         09/01/1987   873072000000
5         09/08/1987   873676800000
6         10/01/1987   875664000000
7         08/01/1987   870393600000
8         08/01/1987   870393600000
9         10/01/1987   875664000000
10        09/01/1987   873072000000

Please let me know if you have any idea how to convert "DealActiveDate" to a more conventional date. Thanks! (I'm not sure SO is the best venue, but I couln't think of any other options!)

Answer 1

Looks like milliseconds since 1960-01-01:

as.POSIXct(874022400000/1000, origin="1960-01-01")
# [1] "1987-09-12 01:00:00 CDT"