[Rd] WISH: set.seed(seed) to produce error if length(seed) != 1 (now silent)

[Duncan Murdoch]

I'd say a more serious problem would be using set.seed(.Random.seed), 
because the first entry codes for RNGkind, it hardly varies at all.  So 
this sequence could really mislead someone:

 > set.seed(.Random.seed)
 > sum(.Random.seed)
[1] 24428993419

# Use it to get a new .Random.seed value:
 > runif(1)
[1] 0.3842704

 > sum(.Random.seed)
[1] -13435151647

# So let's make things really random, by using the new seed as a seed:
 > set.seed(.Random.seed)
 > sum(.Random.seed)
[1] 24428993419

# Back to the original!

Duncan Murdoch


On 17/09/2021 8:38 a.m., Henrik Bengtsson wrote:
>> I’m curious, other than proper programming practice, why?
> 
> Life's too short for troubleshooting silent mistakes - mine or others.
> 
> While at it, searching the interwebs for use of set.seed(), gives
> mistakes/misunderstandings like using set.seed(<double>), e.g.
> 
>> set.seed(6.1); sum(.Random.seed)
> [1] 73930104
>> set.seed(6.2); sum(.Random.seed)
> [1] 73930104
> 
> which clearly is not what the user expected.  There are also a few
> cases of set.seed(<character>), e.g.
> 
>> set.seed("42"); sum(.Random.seed)
> [1] -2119381568
>> set.seed(42); sum(.Random.seed)
> [1] -2119381568
> 
> which works just because as.numeric("42") is used.
> 
> /Henrik
> 
> On Fri, Sep 17, 2021 at 12:55 PM GILLIBERT, Andre
> <Andre.Gillibert using chu-rouen.fr> wrote:
>>
>> Hello,
>>
>> A vector with a length >= 2 to set.seed would probably be a bug. An error message will help the user to fix his R code. The bug may be accidental or due to bad understanding of the set.seed function. For instance, a user may think that the whole state of the PRNG can be passed to set.seed.
>>
>> The "if" instruction, emits a warning when the condition has length >= 2, because it is often a bug. I would expect a warning or error with set.seed().
>>
>> Validating inputs and emitting errors early is a good practice.
>>
>> Just my 2 cents.
>>
>> Sincerely.
>> Andre GILLIBERT
>>
>> -----Message d'origine-----
>> De : R-devel [mailto:r-devel-bounces using r-project.org] De la part de Avraham Adler
>> Envoyé : vendredi 17 septembre 2021 12:07
>> À : Henrik Bengtsson
>> Cc : R-devel
>> Objet : Re: [Rd] WISH: set.seed(seed) to produce error if length(seed) != 1 (now silent)
>>
>> Hi, Henrik.
>>
>> I’m curious, other than proper programming practice, why?
>>
>> Avi
>>
>> On Fri, Sep 17, 2021 at 11:48 AM Henrik Bengtsson <
>> henrik.bengtsson using gmail.com> wrote:
>>
>>> Hi,
>>>
>>> according to help("set.seed"), argument 'seed' to set.seed() should be:
>>>
>>>    a single value, interpreted as an integer, or NULL (see ‘Details’).
>>>
>>>  From code inspection (src/main/RNG.c) and testing, it turns out that
>>> if you pass a 'seed' with length greater than one, it silently uses
>>> seed[1], e.g.
>>>
>>>> set.seed(1); sum(.Random.seed)
>>> [1] 4070365163
>>>> set.seed(1:3); sum(.Random.seed)
>>> [1] 4070365163
>>>> set.seed(1:100); sum(.Random.seed)
>>> [1] 4070365163
>>>
>>> I'd like to suggest that set.seed() produces an error if length(seed)
>>>> 1.  As a reference, for length(seed) == 0, we get:
>>>
>>>> set.seed(integer(0))
>>> Error in set.seed(integer(0)) : supplied seed is not a valid integer
>>>
>>> /Henrik
>>>
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