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rdater-faq

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

Solution

  • 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.