[R] Inserting a new row in a matrix

[culpritNr1]

Hi Alwx99,

Nobody has answered your email, so, I am left with the honour of
disappointing you.

In R, matrices are not dynamically allocated. If you are a C/C++/Fortran/etc
programmer you know what I am talking about.

Lets assume that you are not such programmer. Inserting a row would tell R
to push a little the memory that holds your matrix so that a now row can be
squeezed in. R does not do that, unfortunately. You have to come up with
your own workarounds. 

I suggest that you consider rebuilding your matrix each "for" loop cycle
with an infamous rbind. Something like

for (...blah...) {
    ...blah...
    MatrixWithOneMoreRow <- rbind(PartialMatrixAboveRow, NewRow,
PartialMatrixBelowRow)
}

Sorry. I recently discovered that R is not as modern as me and you expected.
No dynamical matrices. More on this?: search this List with "in-place
appending to a matrix".

PLEASE, somebody, prove me wrong!

Your culpritNr1



Alex99 wrote:
> 
> Hi guys,
> 
> I need to insert a row to a matrix in a for loop. I have matrix named
> "Avg" which is a 5x4 matrix of zeros. 
> I have a file named "A"(4 rows,14 columns) which I make a sample of it 5
> times. each time I get the mean for each column and put the result in the
> "Avg" matrix. this is my code:
> 
> Avg=matrix(0,5,4)
>> 
>>  for(i in 1:5){
> +  res=(A[sample(nrow(A), 5),])
> +  insertRow(Avg,i,colMeans(res))
> +  show(res)
> +  show(Avg)
> +  }
> 
> this is my result(I just copied the first sample) :
> 
>     s1 s2 s3 s4
> 2    1  0  1  0
> 3    0  0  0  0
> 11  0  0  0  0
> 5    0  1  0  1
> 12  0  0  0  0
>      [,1] [,2] [,3] [,4]
> [1,]    0    0    0    0
> [2,]    0    0    0    0
> [3,]    0    0    0    0
> [4,]    0    0    0    0
> [5,]    0    0    0    0
> 
> it's suppose to put .2 .2 .2 .2 in the first row of the matrix but as you
> see it's all 0. any idea why and how to fix it?
> 
> Thanks,
> 
> 

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