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last
2012 Apr 04
2
Selecting obs within groups defined by 2 variables
...y real dataset, C2 is a date (mm/dd/yy)
C1 C2 C3
1 x 1
1 x 2
1 y 1
1 y 2
2 x 1
2 x 2
2 y 1
2 y 2
I have found code (from UCLA R FAQs and this list's archives) for
selecting the last observation when a group is defined by ONE variable
(e.g., C1):
last <-by(mydata, mydata$C1, tail, n=1)
lastd<-do.call("rbind", as.list(last))
The by function does not seem to allow two variables in the Indices
argument:
last <-by(mydata, mydata$C1 mydata$C2, tail, n=1) THIS DOESN'T WORK
I tried creating a new variable C1*C2, but I think this is risky since
it may not be unique de...