[R] x[order(x)] vs sort(x)?

[Rory.WINSTON at rbs.com]

Hi

I have a question (which may be an obvious one). It is about an idiom which I have seen quite often:

o <- order(x); <- x[o]

vs. the alternative

x <- sort(x)

I am just wondering as to the rationale behind the order/reindex idiom vs sorting. Especially as there seems to be a marked performance difference (especially for integer vectors):

> x <- trunc(runif(1E6, 1, 100))
> system.time(y <- x[order(x)])
   user  system elapsed
   1.19    0.01    1.21
> system.time(y <- sort(x))
   user  system elapsed
   0.22    0.00    0.22

I suspect that the propensity for the order/reindex idiom may be related to memory or space performance then, rather than time? Can anyone confirm if this is the case?

Cheers
Rory



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