as.Date with dates in format m/d/y in R

A client sent me an Excel file with dates formatted as e.g 3/15/2012 for March 15. I saved this as a .csv file and then used

camm$Date <- as.Date(camm$Date, "%m/%d/%y")

but this gave me values starting in the year 2020!

I tried to reformat the dates in the original csv file so that they were e.g. 03/14/2013 but was unable to do so.

Any help appreciated

Use capital Y in as.Date call instead. This should do the trick:

> as.Date("3/15/2012", "%m/%d/%Y")
[1] "2012-03-15"

From the help file's examples you can realize when year is full specified you should use %Y otherwise %y for example:

> dates <- c("02/27/92", "02/27/92", "01/14/92", "02/28/92", "02/01/92")
> as.Date(dates, "%m/%d/%y")
[1] "1992-02-27" "1992-02-27" "1992-01-14" "1992-02-28" "1992-02-01"

You can see that in your example the Year format is 2012 then you should use %Y, and in the other example (taken from the as.Date help file) Year format is 92 then using %y is the correct way to go. See as.Date for further details.

You might also give a try to the lubridate package if you do not want to deal with the hieroglyphics :)

> library(lubridate)
> parse_date_time('3/15/2012', 'mdy')
 1 parsed with %m/%d/%Y
[1] "2012-03-15 UTC"

PS.: of course I do not encourage anyone to use any extra dependencies, this answer was just posted here as an alternative (and quick to remeber) solution

To complete the picture, you might also try the recently introduced (2016-09) package anytime which takes advantage of the Boost C++ libraries:

anytime::anytime("3/15/2012")
#[1] "2012-03-15 CET"

We can use mdy from lubridate

lubridate::mdy('3/15/2012')
#[1] "2012-03-15"

Or parse_date from readr which uses same format as as.Date

readr::parse_date('3/15/2012', '%m/%d/%Y')
#[1] "2012-03-15"