> On Apr 4, 2017, at 8:51 AM, Tunga Kantarcı <tungakanta...@gmail.com> wrote: > > I have a data frame. One column (call this column a) contains years, > like 1871, and another column (call this column b) contains months, > like 2. I need to convert these year-month combinations, stored in > these two date vectors, into a single serial date number. E.g. year > 1871 and month 2, stored in different vectors, should return 683429. > Meanwhile, when I check the class type of columns a and b, they are > both integer. > > In MATLAB this can easily be done using the syntax > > output = datenum(a,b,1) > > In R, I have tried the as.POSIXct function but did not succeed. I also > tried the ISOdatetime function but that returned NA for all entries. > It should be a simple operation but I cannot seem to figure it out.
Hi, The standard date classes in R require the full date (day, month, year) and the date/time classes require a correct time as well. Looking at the help page for ?as.Date, there is information pertaining to MATLAB's date origin of 0000-01-01, as compared to R's of 1970-01-01. The difference is an offset of 719529. Taking your number above of 683429, that would yield: > as.Date(683429, origin = "1970-01-01") - 719529 [1] "1871-03-01" So your 'b' should be 3, not 2, presuming the first of the month is inferred. Otherwise: > as.Date(683401, origin = "1970-01-01") - 719529 [1] "1871-02-01" So, to reverse it, would be: a <- 1871 b <- 3 > paste(a, b, 1, sep = "-") [1] "1871-3-1" > as.Date(paste(a, b, 1, sep = "-")) [1] "1871-03-01" > as.numeric(as.Date(paste(a, b, 1, sep = "-"))) + 719529 [1] 683429 The last step takes the date and coerces it to a numeric value in the number of days since the origin. More generally, if you Google for R MATLAB, there are some online references that provide varying levels of function mappings between the two languages that you may find helpful. Regards, Marc Schwartz ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
