Anyway I think it was just a toy example.
Any additionnal information is welcome.
Best,
Jean
2009/11/22 Peter Ehlers <ehl...@ucalgary.ca>
>
>
> Stefan Evert wrote:
>
>> Sure, badly written R code does not perform as well as well written python
>>> code or C code. On the other hand badly written python code does not perform
>>> as well as well written R code.
>>>
>>> What happens when you try one of these :
>>>
>>> sum <- sum( 1:N )
>>>
>>
>> R runs out of memory and crashes. :-) I didn't tell you how big N is, did
>> I?
>>
>
> Really?
>
> N <- 1e30
> sum( 1:N )
> Error in 1:N : result would be too long a vector
>
> -Peter Ehlers
>
>
> >
>
>>
>> But this is exactly the point I was trying to make (but perhaps not
>> prominently enough). In many cases, you can vectorize at least parts of
>> your code or find a more efficient algorithm, which may be faster in R than
>> a brute-force solution in C. But sometimes, you just cannot avoid loops
>> (let's not forget that all the forms of apply() are just loops and don't
>> give much of a speed benefit over a for-loop), function calls, etc.; in this
>> case, performance differences between interpreted languages can matter.
>>
>> Personally, I'd never switch from R to Perl just for speed, though.
>>
>> BTW, I also tried a vectorised algorithm in R, which calculates the sum
>> above in a small number of chunks:
>>
>> N1 <- 50
>>> N2 <- 1000000
>>> N <- N1 * N2
>>> sum <- 0
>>>
>>> for (i in 1:N1) {
>>> x <- as.numeric(i-1) * N2 + 1:N2
>>> sum <- sum + sum(x)
>>> }
>>>
>>
>> which gives
>>
>> R/simple_count_vec.R 31.30 Mops/s (50000000 ops in 1.60 s)
>>
>> So an interpreted loop in Lua is still faster than this partially
>> vectorized code in R:
>>
>> lua/simple_count.lua 65.78 Mops/s (100000000 ops in 1.52 s)
>>>>
>>>
>> As people on the SQLite mailing list always say: there's no general answer
>> as to which language/implementation/query/... is faster and better. You
>> just have to test the different options for your specific application
>> setting, and be prepared for one or two surprises.
>>
>> Just in case this isn't obvious: If I rewrote matrix multiplication in C
>> and linked this code into R, it would run much slower than if I just typed
>> "A %*% B".
>>
>> All the best,
>> Stefan
>>
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>>
>>
>>
> ______________________________________________
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