r - Split date data (m/d/y) into 3 separate columns

Question

I need to convert date (m/d/y format) into 3 separate columns on which I hope to run an algorithm.(I'm trying to convert my dates into Julian Day Numbers). Saw this suggestion for another user for separating data out into multiple columns using Oracle. I'm using R and am throughly stuck about how to code this appropriately. Would A1,A2...represent my new column headings, and what would the format difference be with the "update set" section?

 update <tablename> set A1 = substr(ORIG, 1, 4), 
                       A2 = substr(ORIG, 5, 6), 
                       A3 = substr(ORIG, 11, 6), 
                       A4 = substr(ORIG, 17, 5); 

I'm trying hard to improve my skills in R but cannot figure this one...any help is much appreciated. Thanks in advance... :)

Answer 1

I use the format() method for Date objects to pull apart dates in R. Using Dirk's datetext, here is how I would go about breaking up a date into its constituent parts:

datetxt <- c("2010-01-02", "2010-02-03", "2010-09-10")
datetxt <- as.Date(datetxt)
df <- data.frame(date = datetxt,
                 year = as.numeric(format(datetxt, format = "%Y")),
                 month = as.numeric(format(datetxt, format = "%m")),
                 day = as.numeric(format(datetxt, format = "%d")))

Which gives:

> df
        date year month day
1 2010-01-02 2010     1   2
2 2010-02-03 2010     2   3
3 2010-09-10 2010     9  10

Note what several others have said; you can get the Julian dates without splitting out the various date components. I added this answer to show how you could do the breaking apart if you needed it for something else.