[R] Counter in a For Loop - Efficiency Issue

[Bart Joosen]

without a reproducible sample, it is hard to tell, but I will give it a shot.
Maybe it's possible to merge your M with M2: merge(M, M2)
If you only want to count times, you can use seq_along(x) in a by function
eg:
dat <- data.frame(person=rep(c(1,2,3), each=5), time=rnorm(15))
by(dat$person, dat$person, function(x) seq_along(x))

Ofcourse you can use any of the other vectorisation functions (lapply,
apply, aggregate, ....)

HTH


Bart
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