Is set.seed consistent over different versions of R (and Ubuntu)?

29
votes

I am currently running R version 3.1.0 (on Ubuntu 12.04 LTS) and as both my R version and my operating system is getting rather old, I plan on updating both. However, I have a lot of simulations that rely on set.seed() and I would like them to still give me the same random numbers after updating both R and my operating system.

So my question is three-fold.

  1. Can I update R without changing which numbers are generated from each seed?
  2. Can I do the same for my operating system?
  3. If no to either 1) or 2), is there a way to change the seeds in my code in such a way that they are consistent with the olds seeds?
2
rubunturandom-seed
Random number generation is done using an algorithm. set.seed() passes the seed to it. Hence, it shouldn't depend on OS and R version. So, 1. Yes. 2. Yes. – Suren

2 Answers

58
votes

Cross-OS consistency: yes

If you installed R on two different operating systems without manually changing defaults or the RProfile, you should get the same results when using set.seed().

Consistency over versions of R: not necessarily

It used to be the case that set.seed() would give the same results across R versions, but that's no longer generally true thanks to a little-announced update in R 3.6.0. So you can get cross version consistency comparing results before R 3.6.0, but if you compare a post-3.6.0 use of set.seed() to a pre-3.6.0 use of set.seed(), you will get different results.

You can see that in the examples below:

R 3.2.0

> set.seed(1999)
> sample(LETTERS, 3)
[1] "T" "N" "L"

R 3.5.3

> set.seed(1999)
> sample(LETTERS, 3)
[1] "T" "N" "L"

R 3.6.0

set.seed(1999)
sample(LETTERS, 3)
[1] "D" "Z" "R"

The reason for the inconsistency is that in R 3.6.0, the default kind of under-the-hood random-number generator was changed. Now, in order to get the results from set.seed() to match, you have to first call the function RNGkind(sample.kind = "Rounding").

R 3.6.0

> RNGkind(sample.kind = "Rounding")
Warning message:
In RNGkind(sample.kind = "Rounding") : non-uniform 'Rounding' sampler used
> set.seed(1999)
> sample(Letters, 3)
[1] "T" "N" "L"
3
votes

Having tested on several R versions (3.1.0, 3.3.1, 3.4.2) and two different machines (Windows 7 x64, Windows 10 x64), I got the same runif() random numbers with the same set.seed() independently of the R versions and the operating system. As far as I know, this suggests a yes for both questions 1 and 2.