R Syntax for converting date to SAS date9 format but the date should be numeric and only format should change

Question

Consider that I have a date i.e. 2017-10-23, and want the result to look 23OCT2017

date <- '2017-10-23'

date2 <- toupper(format(as.Date('2017-10-23'),'%d%b%Y'))
str(date2)

chr "23OCT2017"

however this results in character date, however i want that to be numeric but the format should be 23OCT2017. Could any suggest how to accomplish this

Answer 1

R doesn't really have the idea of a "format", which I suspect is something you've got from SAS.

What you can do is create a new class, and write a print method for that class to show the values in anyway you like. For example, if I create:

print.d9 = function(x){
    print(
      toupper(
        format(
         as.Date(unclass(x),origin="1970-01-01"),
         '%d%b%Y')))
}

Then a numeric vector looks like numbers:

> v = c(0, 366, 1000)
> v
[1]    0  366 1000

until I re-class it as "d9":

> class(v) = c("numeric","d9")

and then it prints using the print.d9 function:

> v
[1] "01JAN1970" "02JAN1971" "27SEP1972"

But the underlying data are numeric:

> v
[1] "01JAN1970" "02JAN1971" "27SEP1972"
> v+30
[1] "31JAN1970" "01FEB1971" "27OCT1972"

But this is only half the job, for example as is you can't put these into a data frame and still see the character representation:

> data.frame(x1=v)
    x1
1    0
2  366
3 1000

Yeah there's ways round this, but any sensible code would use native R dates as much as possible and only convert to a specific date format at the last moment. R's date objects are numeric and can be put in data frames, unlike my d9 class above. And you've already written code to convert to the format you want.