[R] lapply or data.table to find a unit's previous transaction

I have a dataset of property transactions that includes the transaction ID (TranID), property ID (UnitID), and transaction date (TranDt). I need to create a data frame (or data table) that includes the previous transaction date, if one exists. This is an easy problem in SQL, where I just run a

[R] Biometric Summit - 2010

/_links.php?id=884] ~~ This email was sent to r-help@r-project.org, by biodig...@swbell.net [ Unsubscribe ] if you no longer wish to receive our mailings. For abuse concerns, please contact ab...@cuemails.com. William Rogers | PO Box

[R] Biometric Summit - Feb. 22-25, 2010

...@cuemails.com. William Rogers | PO Box 510047 | St Louis, MO 510047 [[alternative HTML version deleted]] __ 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