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2010 Jun 03
2
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 sub-query, but I'm trying to make R my one-stop-shopping program. ?The following code works on a subset of my data, but I can't run...