Is there a more elegant way to convert two-digit years to four-digit years with lubridate?

Question

If a date vector has two-digit years, mdy() turns years between 00 and 68 into 21st Century years and years between 69 and 99 into 20th Century years. For example:

library(lubridate)     mdy(c("1/2/54","1/2/68","1/2/69","1/2/99","1/2/04")) 

gives the following output:

Multiple format matches with 5 successes: %m/%d/%y, %m/%d/%Y. Using date format %m/%d/%y. [1] "2054-01-02 UTC" "2068-01-02 UTC" "1969-01-02 UTC" "1999-01-02 UTC" "2004-01-02 UTC" 

I can fix this after the fact by subtracting 100 from the incorrect dates to turn 2054 and 2068 into 1954 and 1968. But is there a more elegant and less error-prone method of parsing two-digit dates so that they get handled correctly in the parsing process itself?

Update: After @JoshuaUlrich pointed me to strptime I found this question, which deals with an issue similar to mine, but using base R.

It seems like a nice addition to date handling in R would be some way to handle century selection cutoffs for two-digit dates within the date parsing functions.

Answer 1

Here is a function that allows you to do this:

library(lubridate) x <- mdy(c("1/2/54","1/2/68","1/2/69","1/2/99","1/2/04"))   foo <- function(x, year=1968){   m <- year(x) %% 100   year(x) <- ifelse(m > year %% 100, 1900+m, 2000+m)   x } 

Try it out:

x [1] "2054-01-02 UTC" "2068-01-02 UTC" "1969-01-02 UTC" "1999-01-02 UTC" [5] "2004-01-02 UTC"  foo(x) [1] "2054-01-02 UTC" "2068-01-02 UTC" "1969-01-02 UTC" "1999-01-02 UTC" [5] "2004-01-02 UTC"  foo(x, 1950) [1] "1954-01-02 UTC" "1968-01-02 UTC" "1969-01-02 UTC" "1999-01-02 UTC" [5] "2004-01-02 UTC" 

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The bit of magic here is to use the modulus operator %% to return the fraction part of a division. So 1968 %% 100 yields 68.