[R] small object but huge RData file exported

[Duncan Murdoch]

On 20/10/2021 8:57 a.m., Jinsong Zhao wrote:
> Hi there,
> 
> I have a RData file that is obtained by save.image() with size about
> 74.0 MB (77,608,222 bytes).
> 
> When load into R, I measured the size of each object with object.size():
> 
>> object.size(combn.rda.m)
> 105448 bytes
>> object.size(cross)
> 102064 bytes
>> object.size(denitr.1)
> 25032 bytes
>> object.size(rda.denitr.1)
> 600280 bytes
>> object.size(xh)
> 7792 bytes
>> object.size(xh.x)
> 6064 bytes
>> object.size(xh.x.1)
> 24144 bytes
>> object.size(xh.x.2)
> 24144 bytes
>> object.size(xh.x.3)
> 24144 bytes
>> object.size(xh.y)
> 2384 bytes
> 
> There are all small objects.
> 
> If I delete the largest one "rda.denitr.1", and save.image("xx.RData").
> It has the size of 22.6 KB (23,244 bytes). All seem OK.
> 
> However, when I save(rda.denitr.1, file = "yy.RData"), then it has the
> size of 73.9 MB (77,574,869 bytes).
> 
> I don't know why...
> 
> Any hint?

As the docs for object.size() say, "Exactly which parts of the memory 
allocation should be attributed to which object is not clear-cut."  In 
particular, if a function or formula has an associated environment, it 
isn't included, but it is sometimes saved in the image.

So I'd suspect rda.denitr.1 contains something that references an 
environment, and it's an environment that would be saved.  (I forget the 
exact rules, but I think that means it's not the global environment and 
it's not a package environment.)

Duncan Murdoch