[R] Initializing vector and matrices
Steven Yen
@tyen @end|ng |rom ntu@edu@tw
Thu Feb 29 15:39:12 CET 2024
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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