To R-Sig-Insurance: The mondate package enables date arithmetic in units of 'months' and 'years', not available with the base 'difftime' function. This can be particularly helpful for calculating the actuarial age of property/casualty/general insurance liabilities. Update ...04 expands the signature of the year, month, and day functions to Date and POSIXt data. See NEWS at cran.r-project.org/web/packages/mondate/index.html. An example of using mondate is
library(mondate)
mondate(as.Date("2013-03-31")) - mondate(as.Date("2013-02-28"))
[1] 1 A potential future package enhancement would be to extend 'difftime' so that the following functionality is possible
difftime(as.Date("2013-03-31"), as.Date("2013-02-28"), units = "months")
Time difference of 1 month For more information on mondate, visit http://code.google.com/p/mondate/ Dan Murphy