# Random number generator seed in R

I have a question about the random number generator seed number in R. Recently, I am trying to solve the exercises in the book named "An Introduction to Statistical Learning". When I following the practices, I found pretty odd situation. Although I set a same seed number, the result is slightly different from the book.

So, my question is that is it possible that a same seed number results in a different result? I think, it could result from the version of my R (or due to the fact that I am using R studio and the book employed GNU R)

• Can you refer more precisely to the exercise. Which function or set of commands is generating a different answer? Apr 1, 2021 at 7:03
• Given my answer, were the differences of the same order? Apr 1, 2021 at 12:33

Looking at the first page (first edition) with set.seed() commands,

I was able to reproduce the outcome, using R version 3.4.4 (2018-03-15). (R studio produces exactly the same.)

> set.seed(1303)
> rnorm(10)
[1] -1.1439763145  1.3421293656  2.1853904757  0.5363925179  0.0631929665
[6]  0.5022344825 -0.0004167247  0.5658198405 -0.5725226890 -1.1102250073


and

> set.seed(3)
> y=rnorm(100)
> mean(y)
[1] 0.01103557
> var(y)
[1] 0.7328675
> sqrt(var(y))
[1] 0.8560768
> sd(y)
[1] 0.8560768


the only difference being the excessive precision in my R output. Note the warning in the text about possible discrepancies occuring with new versions of R.

• That's a good point. The OP's "slightly different" may simply be different output precisions. +1. Mar 31, 2021 at 14:41

The seed should make your analysis fully reproducible. I would much rather assume that differences in R (and package) versions, or a bug in your (or the book's) code, or possibly even machine/OS differences would be responsible for any discrepancies. (Converted from a comment.)