How to convert month-year data to POSIX date format

parse_month_year.R

# some data specifying the month and year
month <- c( "Sep-10", 
            "Oct-10",
            "Nov-10",
            "Jan-11")

# It would appear that strptime and related
# as.POSIXct functions require there to be a
# day specified. Here I prepend the month-year
# data with the first day.
dd <- paste( 1, month, sep="" )

# then use strptime to convert to a full POSIX
# date format.
# %d reads in the da
# %b- reads in the abbreviated month followed by "-"
# %y reads in the year without century.
# NB it uses the current locale to add the timezone
# and in this case seems to be taking account of d
# daylight savings time  by differentiating between
# BST and GMT

mm <- strptime(dd, format = "%d%b-%y")

print(mm)