Difference between paste and paste0:
> (nth <- paste0(1:12, c("st", "nd", "rd", rep("th", 9))))
[1] "1st"? "2nd"? "3rd"? "4th"? "5th"? "6th"? "7th"? "8th"? "9th"? "10th"
[11] "11th" "12th"
> (nth <- paste(1:12, c("st", "nd", "rd", rep("th", 9))))
[1] "1 st"? "2 nd"? "3 rd"? "4 th"? "5 th"? "6 th"? "7 th"? "8 th"? "9 th"
[10] "10 th" "11 th" "12 th"