R use ddply or aggregate

Question

I have a data frame with 3 columns: custId, saleDate, DelivDateTime.

> head(events22)
     custId            saleDate      DelivDate
1 280356593 2012-11-1         


        

Answer 1

This should be pretty fast but data.table is likely faster:

do.call(rbind, 
    lapply(split(events22, events22$custId), function(x){
        x[which.max(x$saleDate), ]
    })
)