[R] Fw: efficiently replacing values in a matrix

[Nnamdi]

----- Forwarded Message ----
From: Nnamdi <nnamdii at yahoo.com>
To: roger koenker <rkoenker at uiuc.edu>
Sent: Friday, April 18, 2008 1:08:58 PM
Subject: Re: [R] efficiently replacing values in a matrix


I tried the sparse matrix implementation, still there are issues:

a <- matrix(nrow=10000,ncol=10000)
> a.csr <- as.matrix.csr(a)
Error in if (nnz == 0) { : missing value where TRUE/FALSE needed

I'm guessing this error here is because 'a' matrix is initialized with'NA's. Yet when I try initializing 'a' matrix with 0s I get:
> a<-matrix(nrow=10000,ncol=10000,rep(0,10000*10000))
Error: cannot allocate vector of size 762.9 Mb

Either way I cannot achieve my goal of being able to efficiently enter values into this matrix.

To answer your previous question, this matrix is somewhat dense. It is a symmetrical matrix thus only the upper triangle is filled.

Any other ideas? Thanks again

--Nnamdi


----- Original Message ----
From: roger koenker <rkoenker at uiuc.edu>
To: Nnamdi <nnamdii at yahoo.com>
Sent: Friday, April 18, 2008 12:25:54 PM
Subject: Re: [R] efficiently replacing values in a matrix

is this really a dense matrix?  if not, then sparse representations
would be much more efficient...

url:    www.econ.uiuc.edu/~roger            Roger Koenker
email    rkoenker at uiuc.edu            Department of Economics
vox:     217-333-4558                University of Illinois
fax:       217-244-6678                Champaign, IL 61820


On Apr 18, 2008, at 12:11 PM, Nnamdi wrote:

>
> Still it is pretty slow when entering values into a large matrix.  
> Case in
> point:
>
>> a <- matrix(nrow=10000,ncol=10000)
>> system.time(a[1,1] <- 1903908.80385)
>   user  system elapsed
> 30.840   6.226  41.416
>> is.matrix(a)
> [1] TRUE
>
> Is there a better way to enter values into large matrices? If I have  
> to
> spend 41 secs each time I enter into a cell and I have 10000x10000  
> cells to
> enter that is impractical!
>
> --Nnamdi
>
> Rolf Turner-3 wrote:
>>
>>
>> On 17/04/2008, at 9:33 AM, Charles C. Berry wrote:
>>
>>     <snip>
>>
>>> I'll lay odds that Matthew's 'matrix' is actually a data.frame, and
>>> I'll not be surprised if the columns are factors.
>>
>>     <snip>
>>
>> I suspect that you're right.
>>
>> ***Why*** can't people distinguish between data frames and matrices?
>> If they were the same <expletive deleted> thing, there wouldn't be  
>> two
>> different terms for them, would there?
>>
>>     cheers,
>>
>>         Rolf Turner
>>
>> ######################################################################
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>
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