As.Date with Two-Digit Years

as.Date with two-digit years

x = format(as.Date("10.10.61", "%d.%m.%y"), "19%y-%m-%d")
x = as.Date(x)
x
class(x)

Reading Dates with two digit years in R

The zoo package is helpful for this:

require(zoo)

x <- as.yearmon("Jan-84", format = "%b-%y")

The lines above first convert the input to class yearmon:

"Jan 1984"

From there you can convert the yearmon class to Date (or POSIXct), like this:

x <– as.Date(x)

Now the object is of class Date:

"1984-01-01"

Define year for two digits year date format

We can create a function to do this

library(lubridate)
f1 <- function(x, year=1970){
   x <- dmy(x)
   m <- year(x) %% 100
   year(x) <- ifelse(m > year %% 100, 2000+m, 1900+m)
  x
}

f1(character_date)
#[1] "1944-01-19"

---

If this always have 19 as prefix for year

dmy(sub("-(\\d+)", "-19\\1", character_date))
#[1] "1944-01-19"

as.date converting dates to the wrong year

Use this format instead:
mbt2$t <- as.Date(mbt2$t , format = "%d/%m/%Y")

%y is 2-digit year, while %Y is 4-digit year. Your version reads just first 2 digits from 1957 and that's why it returns 2019.

Converting 2 digit date year in string to a Date Object

This seems not be implemented (yet). See the discussion here or the (open) pull request to implement it here.

It is a debated topic, as the default in other languages is to assign years >68 to the twenty century and those <=68 to the twenty-first century, that is a bit subjective, so the Julia developers preferred to go for the explicit way that the missing digits must be explicitly added.

So for now just add 2000 years:

t2 = "27/01/17"
Date(t2, "dd/mm/yy") + Dates.Year(2000)

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

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"

---

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

Character 2 digit year conversion to year only

Not elegant. But using combination of lubridate and as.Date you can get that.

library(lubridate)
data <- data.frame(variable = c(95, 96, 97,98,99), date=c(1,2,3,4,5))
data$variableUpdated <- year(as.Date(as.character(data$variable), format="%y"))

and only with base R

data$variableUpdated <- format(as.Date(as.character(data$variable), format="%y"),"%Y")

---

Related Topics