> Date
"2012-01-01 UTC"
"2013-01-01 UTC"

> week(Date)
1
1

> result of awesome R code here
1
54

tda - min(tda)

(tda - min(tda))/eweeks(1)

tda - ymd(19960101)

(tda - ymd(19960101))/eweeks(1)

trunc((tda - ymd(20111225))/eweeks(1))

tda = ymd(c(20120101, 20120106, 20130101, 20130108))

1  1 53 54

week(dat) +53*(year(dat)-min(year(dat)))

weeknos <- (interval(min(tda), tda) %/% weeks(1)) + 1