Extract date elements from POSIXlt and put into data frame in R

Try this (DF as your data.frame):

extractdate <- function(date) {
    day <- format(date, format="%d")
    month <- format(date, format="%m")
    year <- format(date, format="%Y")

    cbind(day, month, year)
}

cbind(DF, extractdate(DF$dd_mmm_yy))

If you are using the data.table package, it already has functions to extract data time components from POSIXct.

second(x)
minute(x)
hour(x)
yday(x)
wday(x)
mday(x)
week(x)
isoweek(x)
month(x)
quarter(x)
year(x)

The use is straightforward (e.g. dt[, day := day(dd_mmm_yy)]). You can see the full documentation here.

POSIXlt objects are a list of 9 components (see the Details section of ?POSIXlt for more information). Because the dd_mmm_yy column is POSIXlt, you don't need a function to extract the components. You can just extract the components by their names:

orders$day <- orders$dd_mmm_yy$mday        # day of month
orders$month <- orders$dd_mmm_yy$mon+1     # month of year (zero-indexed)
orders$year <- orders$dd_mmm_yy$year+1900  # years since 1900
orders
#   order_id  dd_mmm_yy day month year
# 1        1 2005-07-28  28     7 2005
# 2        2 2007-03-04   4     3 2007

One liner using lubridate

require(plyr); require(lubridate)
mutate(mydf, date = ymd(dd_mmm_yy), day = day(date), 
  month = month(date), year = year(date))

  order_id  dd_mmm_yy       date day month year
1        1 2005-07-28 2005-07-28  28     7 2005
2        2 2007-03-04 2007-03-04   4     3 2007