Two things: 1. You need to convert the result of the paste() to a Date related class.
2. R's standard Date classes require a full date, so you would have to add in some default day of the month: See ?as.Date NewDate <- as.Date(paste(month.abb[as.numeric(ddf$month)], "01", ddf$Year, sep="-"), format = "%b-%d-%Y") or without using month.abb, which is not really needed. Note the difference in the format argument: NewDate <- as.Date(paste(as.numeric(ddf$month), "01", ddf$Year, sep="-"), format = "%m-%d-%Y") > class(NewDate) [1] "Date" > str(NewDate) Date[1:12], format: "1999-01-01" "1999-02-01" "1999-03-01" "1999-04-01" ... You can then format the output of NewDate as you might require: > format(NewDate, format = "%b-%d-%Y") [1] "Jan-01-1999" "Feb-01-1999" "Mar-01-1999" "Apr-01-1999" [5] "May-01-1999" "Jun-01-1999" "Jul-01-1999" "Aug-01-1999" [9] "Sep-01-1999" "Oct-01-1999" "Nov-01-1999" "Dec-01-1999" Note that the output of the last step is a character vector: > str(format(NewDate, format = "%b-%d-%Y")) chr [1:12] "Jan-01-1999" "Feb-01-1999" "Mar-01-1999" ... which is fine for formatting/printing, even though NewDate is a Date class object. Alternatively, I believe that Gabor's 'zoo' package on CRAN has a 'yearmon' class for this type of partial date. Regards, Marc On Sep 23, 2014, at 12:04 PM, Kuma Raj <pollar...@gmail.com> wrote: > Many thanks for your quick answer which has created what I wished. May > I ask followup question on the same issue. I failed to convert the new > column into date format with this code. The class of MonthDay is still > character > > df$MonthDay <- format(df$MonthDay, format=c("%b %Y")) > I would appreciate if you could suggest a working solution > Thanks > > > On 23 September 2014 18:03, Marc Schwartz <marc_schwa...@me.com> wrote: >> On Sep 23, 2014, at 10:41 AM, Kuma Raj <pollar...@gmail.com> wrote: >> >>> Dear R users, >>> >>> I have a data with month and year columns which are both characters >>> and wanted to create a new column like Jan-1999 >>> with the following code. The result is all NA for the month part. What >>> is wrong with the and what is the right way to combine the two? >>> >>> ddf$MonthDay <- paste(month.abb[ddf$month], ddf$Year, sep="-" ) >>> >>> >>> Thanks >>> >>>> dput(ddf) >>> structure(list(month = c("01", "02", "03", "04", "05", "06", >>> "07", "08", "09", "10", "11", "12"), Year = c("1999", "1999", >>> "1999", "1999", "1999", "1999", "1999", "1999", "1999", "1999", >>> "1999", "1999"), views = c(42, 49, 44, 38, 37, 35, 38, 39, 38, >>> 39, 38, 46), MonthDay = c("NA-1999", "NA-1999", "NA-1999", "NA-1999", >>> "NA-1999", "NA-1999", "NA-1999", "NA-1999", "NA-1999", "NA-1999", >>> "NA-1999", "NA-1999")), .Names = c("month", "Year", "views", >>> "MonthDay"), row.names = 109:120, class = "data.frame") >>>> >>> >> >> >> >> Since you are trying to use ddf$month as an index into month.abb, you will >> either need to coerce ddf$month to numeric in your code, or adjust how the >> data frame is created. >> >> In the case of the former approach: >> >>> paste(month.abb[as.numeric(ddf$month)], ddf$Year, sep="-" ) >> [1] "Jan-1999" "Feb-1999" "Mar-1999" "Apr-1999" "May-1999" "Jun-1999" >> [7] "Jul-1999" "Aug-1999" "Sep-1999" "Oct-1999" "Nov-1999" "Dec-1999" >> >> >> Regards, >> >> Marc Schwartz >> ______________________________________________ R-help@r-project.org mailing list 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.