[R] About R memory management?

[Peng Yu]

I have a situation that I can not predict the final result's dimension.

In C++, I believe that the class valarray could preallocate some
memory than it is actually needed (maybe 2 times more). The runtime
for a C++ equivalent (using append) to the R code would still be C*n,
where C is a constant and n is the length of the vector. However, if
it just allocate enough memory, the run time will be C*n^2.

Based on your reply, I suspect that R doesn't allocate some memory
than it is currently needed, right?

On Fri, Dec 11, 2009 at 11:22 AM, Henrik Bengtsson <hb at stat.berkeley.edu> wrote:
> Related...
>
> Rule of thumb:
> Pre-allocate your object of the *correct* data type, if you know the
> final dimensions.
>
> /Henrik
>
> On Thu, Dec 10, 2009 at 8:26 AM, Peng Yu <pengyu.ut at gmail.com> wrote:
>> I'm wondering where I can find the detailed descriptions on R memory
>> management. Understanding this could help me understand the runtime of
>> R program. For example, depending on how memory is allocated (either
>> allocate a chuck of memory that is more than necessary for the current
>> use, or allocate the memory that is just enough for the current use),
>> the performance of the following program could be very different.
>> Could somebody let me know some good references?
>>
>> unsorted_index=NULL
>> for(i in 1:100) {
>>  unsorted_index=c(unsorted_index, i)
>> }
>> unsorted_index
>>
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>>
>