[R] Large loops in R

[Charles Novaes de Santana]

On Tue, Dec 4, 2012 at 8:43 PM, Peter Langfelder
<peter.langfelder at gmail.com> wrote:
> On Tue, Dec 4, 2012 at 11:27 AM, Charles Novaes de Santana
> <charles.santana at gmail.com> wrote:
>> Dear Michael,
>>
>> Thank you for your answer.
>>
>> I have 2 matrices. Each position of the matrices is a weight. And I
>> need to calculate the following sum of differences:
>>
>> Considering:
>> mat1 and mat2 - two matrices (each of them 48000 x 48000).
>> d1 and d2 - two constant values.
>>
>> sum<-0;
>> for(i in 1:nrows1){
>>                         for(j in 1:nrows2){
>>                                         sum<-sum+ ( ( (mat1(i,j)/d1) -
>> (mat2(i,j)/d2) )^2 )
>>                                 }
>>                         }
>>                 }
>>
>> I was wondering if there is a better way to do this sum.
>
> sum( (mat1/d1-mat2/d2)^2)
>
> Correct me if I'm wrong though - aren't matrices of 48x times 48k
> larger than what R can handle at present?
>
> HTH
>
> Peter

hmmm I didn't know that the limitation of R was below this value. I
found this error message:

"Error in matrix(0, 48000, 48000) : too many elements specified"

but I thought it was a machine limitation (and I was asking for access
to a better machine in my labs...). Thanks for clarifying it.

Well, when Sarah gave me the answer for my problem, I got a new one :)
Thank you, Sarah and Peter.

So, is there any other way to "trick R" and allocate such large matrices?

Best,

Charles
-- 
Um axé! :)

--
Charles Novaes de Santana
http://www.imedea.uib-csic.es/~charles
PhD student - Global Change
Laboratorio Internacional de Cambio Global
Department of Global Change Research
Instituto Mediterráneo de Estudios Avanzados(CSIC/UIB)
Calle Miquel Marques 21, 07190
Esporles - Islas Baleares - España

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