Return Various Periods from a Dates Object
DESCRIPTION:
Create an ordered factor from a vector of dates according to various calendar periods.
USAGE: 
days(x)
weekdays(x, abb=T)
months(x, abb=T)
quarters(x, abb=T)
years(x)
REQUIRED ARGUMENTS:
x:
a dates object.
OPTIONAL ARGUMENTS:
abb:
logical flag telling whether abbreviations should be returned for days of the week, month names, or quarters. Default is TRUE.
VALUE:
an ordered factor corresponding to days, weekdays, months, quarters, or years of x for the respective function.
DETAILS:
the levels of days are the days of the month, 1 through 31; the levels of weekdays are Sunday through Saturday; the levels of months are January through December; and the levels of quarters are I < II < III < IV if abb=F and 1Q < 2Q < 3Q < 4Q if abb=T. The levels of years are exactly the years of the dates in x---years in the range of x that are not in x itself are not interpolated.
SEE ALSO:
dates , julian , plot .
EXAMPLES: 
# creates a sample dates object of julian dates
x <- c(10,11,12,42,44,45,101,102,212,213,214,300)
dts <- dates(x)


# identifies a weekday or month with each julian day
weekdays(dts)
months(dts)


# produces barplot of # of days in x appearing on particular
# weekday or month
plot(weekdays(dts))
plot(months(dts))


# produces boxplots of julian date by weekday or month
plot(weekdays(dts), x)
plot(months(dts), x)