Stata 12 introduced business calendar format. Business dates are
integer numbers in a certain range of days, weeks, months or years. In this
range some days are omitted (e.g. weekends or holidays). If a business
calendar was created, a stbcal file matching this calendar was created. This
file is required to read the business calendar. This parser reads the stbcal-
file and returns a data.frame with dates matching business calendar dates.
A dta-file containing Stata business dates imported with read.stata13() shows
in formats which stdcal file is required (e.g. "
sp500.stbcal).
Stata allows adding a short description called purpose. This is added as an
attribute of the resulting data.frame.