R help - Feb 2016 - does save.image() also save the random state?

Dear there,

Here is a snipped code,

 > rm(list = ls())
 > x <- 123
 > save.image("abc.RData")
 > rm(list = ls())
 > load("abc.RData")
 > sample(10)
  [1]  3  7  4  6 10  2  5  9  8  1
 > rm(list = ls())
 > load("abc.RData")
 > sample(10)
  [1]  3  7  4  6 10  2  5  9  8  1

you will see that, after loading a abc.RData file that is saved by 
save.image(), sample(10) gives the same results. I am wondering whether 
it's designed purposely. And if it is, how can I get a different results 
of sample(10) every time after loading the saved image?

Any help will be really appreciated. Thanks in advance.

Best,
Jinsong

On 05/02/2016 11:14 AM, Jinsong Zhao wrote:
> Dear there,
>
> Here is a snipped code,
>
>   > rm(list = ls())
>   > x <- 123
>   > save.image("abc.RData")
>   > rm(list = ls())
>   > load("abc.RData")
>   > sample(10)
>    [1]  3  7  4  6 10  2  5  9  8  1
>   > rm(list = ls())
>   > load("abc.RData")
>   > sample(10)
>    [1]  3  7  4  6 10  2  5  9  8  1
>
> you will see that, after loading a abc.RData file that is saved by
> save.image(), sample(10) gives the same results. I am wondering whether
> it's designed purposely. And if it is, how can I get a different
results
> of sample(10) every time after loading the saved image?
This happens because you are reloading the random number seed.  You can 
tell R to ignore it by calling

set.seed(NULL)

just after you load the image.  See ?set.seed for more details.

Duncan Murdoch

On 02/05/2016 05:25 PM, Duncan Murdoch wrote:
> On 05/02/2016 11:14 AM, Jinsong Zhao wrote:
>> Dear there,
>>
>> Here is a snipped code,
>>
>>   > rm(list = ls())
>>   > x <- 123
>>   > save.image("abc.RData")
>>   > rm(list = ls())
>>   > load("abc.RData")
>>   > sample(10)
>>    [1]  3  7  4  6 10  2  5  9  8  1
>>   > rm(list = ls())
>>   > load("abc.RData")
>>   > sample(10)
>>    [1]  3  7  4  6 10  2  5  9  8  1
>>
>> you will see that, after loading a abc.RData file that is saved by
>> save.image(), sample(10) gives the same results. I am wondering whether
>> it's designed purposely. And if it is, how can I get a different
results
>> of sample(10) every time after loading the saved image?
>
> This happens because you are reloading the random number seed.  You can
> tell R to ignore it by calling
>
> set.seed(NULL)
>
> just after you load the image.  See ?set.seed for more details.
>
> Duncan Murdoch
>
Based on your problem description, it seems that you actually do not 
want to restore the whole workspace but only the objects that you worked 
with. If this is indeed the case, it is much better to use 
save(list=ls(), file = "abc.RData") instead of
save.image("abc.RData").
(Actually it is almost always better to use an explicitly parametrized 
save() call instead of save.image()).

save.image() can cause a lot of troubles besides the one you faced 
recently (which is caused due to the save and restore of the 
.Random.seed hidden object, as Duncan mentioned).

Cheers,
Denes



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