[R] Initializing vector and matrices

[Steven Yen]

Thanks to all. Great ideas. I found Eik Vettorazzi's suggesstion easy to 
implrment:

ebarm<-vbarm<-NULL
...

if (is.null(ebarm)) ebarm<-ame.00$ei/k else ebarm<-ebarm+ame.00$ei/k
if (is.null(vbarm)) vbarm<-ame.00$vi/k else vbarm<-vbarm+ame.00$vi/k
...

Steven Yen

On 2/29/2024 10:31 PM, Ebert,Timothy Aaron wrote:

> You could declare a matrix much larger than you intend to use. This works with a few megabytes of data. It is not very efficient, so scaling up may become a problem.
> m22 <- matrix(NA, 1:600000, ncol=6)
>
> It does not work to add a new column to the matrix, as in you get an error if you try m22[ , 7] but convert to data frame and add a column
>
> m23 <- data.frame(m22)
> m23$x7 <- 12
>
> The only penalty that I know of to having unused space in a matrix is the amount of memory it takes. One side effect is that your program may have a mistake that you would normally catch with a subscript out of bounds error but with the extra space it now runs without errors.
>
> Tim
>
>
>
> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Richard O'Keefe
> Sent: Thursday, February 29, 2024 5:29 AM
> To: Steven Yen <styen using ntu.edu.tw>
> Cc: R-help Mailing List <r-help using r-project.org>
> Subject: Re: [R] Initializing vector and matrices
>
> [External Email]
>
> x <- numeric(0)
> for (...) {
>      x[length(x)+1] <- ...
> }
> works.
> You can build a matrix by building a vector one element at a time this way, and then reshaping it at the end.  That only works if you don't need it to be a matrix at all times.
> Another approach is to build a list of rows.  It's not a matrix, but a list of rows can be a *ragged* matrix with rows of varying length.
>
> On Wed, 28 Feb 2024 at 21:57, Steven Yen <styen using ntu.edu.tw> wrote:
>> Is there as way to initialize a vector (matrix) with an unknown length
>> (dimension)? NULL does not seem to work. The lines below work with a
>> vector of length 4 and a matrix of 4 x 4. What if I do not know
>> initially the length/dimension of the vector/matrix?
>>
>> All I want is to add up (accumulate)  the vector and matrix as I go
>> through the loop.
>>
>> Or, are there other ways to accumulate such vectors and matrices?
>>
>>   > x<-rep(0,4)  # this works but I like to leave the length open  >
>> for (i in 1:3){
>> +  x1<-1:4
>> +  x<-x+x1
>> + }
>>   > x
>> [1]  3  6  9 12
>>
>>   > y = 0*matrix(1:16, nrow = 4, ncol = 4); # this works but I like to
>> leave the dimension open
>>        [,1] [,2] [,3] [,4]
>> [1,]    0    0    0    0
>> [2,]    0    0    0    0
>> [3,]    0    0    0    0
>> [4,]    0    0    0    0
>>   > for (i in 1:3){
>> +   y1<-matrix(17:32, nrow = 4, ncol = 4)
>> +   y<-y+y1
>> + }
>>   > y
>>        [,1] [,2] [,3] [,4]
>> [1,]   51   63   75   87
>> [2,]   54   66   78   90
>> [3,]   57   69   81   93
>> [4,]   60   72   84   96
>>   >
>>
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