On 09/05/2019 9:15 a.m., Ulrike Grömping wrote:
Dear R package authors,
I am currently struggling with differences in test results between R
versions 3.5.3 and 3.6.0: There are expected ones (from the new behavior
of sample(), which can be switched off by
RNGkind(sample.kind="Rounding")) and unexpected ones: The normal random
numbers from a call "y <- rnorm(36)" have changed between R versions, in
spite of working with a seed. Consequently, most other outcomes change
as well, as they depend on those random numbers.
Does anyone have an idea what this behavior results from ? You see
samples below (ignore the first columns, these can be made alike by
changing sample.kind; but the normal random numbers in the last column
were the bottom ones before version 3.6.0 and are the top ones afterwards.
< 1 200 10 -25 -2.07823754
< 2 150 30 25 0.48522682
< 3 200 20 -25 0.69676878
...
1 250 10 -15 -0.820426525
2 200 10 -25 -1.238082813
3 100 10 15 -1.199567511
...
Can anyone explain, why this is the case, or how I could possibly
circumvent it (for some noLD checks)?
I am not seeing a difference in rnorm(), but I would expect to see one
if the new sample() code was used, as it can make a different number of
calls to the underlying RNG.
That is: I'd expect this code to give identical results in both
versions, whether I used val <- 10 or any other value:
val <- 10
set.seed(val)
rnorm(36)
This code does not give identical results, because the calls to sample()
will result in different changes to the seed:
val <- 10
set.seed(val)
discard <- sample(1000, 100)
rnorm(36)
Duncan Murdoch
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