{survival}R Documentation

Convert to Julian Dates


Given a month, day, and year, returns the number of days since January 1, 1960.

Usage, day, year, nineteen = TRUE, fillday = FALSE,
         fillmonth = FALSE)


month vector of months.
day vector of days.
year vector of years.
nineteen if TRUE, year values between 0 and 99 are assumed to be in the 20th century A.D.; otherwise, if FALSE, they are assumed to be in the 1st century A.D.
fillday if TRUE, then missing days are replaced with 15.
fillmonth if TRUE, then a missing month causes the month and day to be set to 7/1.


The date functions are particularly useful in computing time spans, such as number of days on test, and similar functions can be found in other statistical packages. The baseline date of Jan 1, 1960 is, of course, completely arbitrary (it is the same one used by SAS).

The fillday and fillmonth options are perhaps useful only to the author and a very few others: we sometimes deal with patients whose birth date was in the 1800's, and only the month or even only the year is known. When the interval is greater than 80 years, a filler seems defensible.


a vector of Julian dates.


Press, W. H., Teukolsky, S. A., Vetterling, W. T., and Flannery, B. P. (1992). Numerical Recipes: The Art of Scientific Computing (Second Edition). Cambridge University Press.

See Also

date.mmddyy, date.ddmmmyy, date.mmddyyyy

Examples, 10, 53)
xzt <-1:10
xzy <-
test <- data.frame(x = xzt, date = xzy)

[Package survival version 2.17 Index]