[R] How to combine character month and year columns into one column

[Marc Schwartz]

On Sep 23, 2014, at 10:41 AM, Kuma Raj <pollaroid at 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