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I am in the process of switching from SAS over to R. I am working on very large CSV datasets that contain vehicle information. As I am processing the data, I need to select the first (or sometimes the second) record (by date) for any records that have the same license plate number. In SAS, there is a function called 'first.' that can be used on sorted datasets to pull out those first

I am new to R, but have been using SAS for years. In this transition period, I am finding myself pulling my hair out to do some of the simplest things. An example of this is that I need to generate a new variable based on the outcome of several existing variables in a data row. In other words, if the variable in all three existing columns are "Yes", then then the new variable should