操作 lubridate 的日期和时间

date <- now()
date
## "2016-07-22 03:42:35 IST"

year(date)
## 2016

minute(date)
## 42

wday(date, label = T, abbr = T)
# [1] Fri
# Levels: Sun < Mon < Tues < Wed < Thurs < Fri < Sat

day(date) <- 31
## "2016-07-31 03:42:35 IST"

# If an element is set to a larger value than it supports, the difference
#  will roll over into the next higher element
day(date) <- 32
## "2016-08-01 03:42:35 IST"