Help interpreting/converting odd date format

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 do开发者_如何学JAVAcumentation, 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!)

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Looks like milliseconds since 1960-01-01:

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