#day.of.week() returns a number between 0 and 6 to
#specify day of the week–0 refers to Sunday.

library(chron)
print(day.of.week(2,8,2010))   #1
print(day.of.week(2,9,2010))   #2
print(day.of.week(2,10,2010))  #3
print(day.of.week(2,11,2010))  #4
print(day.of.week(2,12,2010))  #5
print(day.of.week(2,13,2010))  #6
print(day.of.week(2,14,2010))  #0
print(day.of.week(2,15,2010))  #1

weekdays(x)    #返回星期几后者
format(x,'%w')   #0-6 0代表周日