R converting a factor YYYY-MM to a date

Question

I have a dataframe with a date in the form YYYY-MM, class factor and I am trying to convert it to class date.

I tried:

Date <- c(\"2015-08\",\"201         


        

Answer 1

1) Convert the dates to zoo's "yearmon" class and then to "Date" class:

> library(zoo)
> transform(df, Date = as.Date(as.yearmon(Date)))
        Date Val
1 2015-08-01   1
2 2015-09-01   2
3 2015-08-01   3

The question did not specify which date to convert to so we used the first of the month. Had the last of the month been wanted we could have used this instead:

transform(df, Date = as.Date(as.yearmon(Date), frac = 1))

2) Another possibility not using zoo is to just add the day of the month yourself and then convert to "Date" class.

> transform(df, Date = paste(Date, 1, sep = "-"))
        Date Val
1 2015-08-01   1
2 2015-09-01   2
3 2015-08-01   3

3) Alternately, might want to just use "yearmon" directly since that directly models year and month with no day.

> library(zoo)
> transform(df, Date = as.yearmon(Date))
      Date Val
1 Aug 2015   1
2 Sep 2015   2
3 Aug 2015   3

Note: Do not use "POSIXct" class as this gives a time zone dependent result that can cause subtle errors if you are not careful. A date in one time zone is not necessarily the same as in another time zone.