Dear Steven,
I used "sample" just to generate a non-trivial example, you could insert
your code of generating the real xi at this point :-)
If you want to stick to for-loops for some reasons, something like this
could work
x<-NULL
for (i in 1:5){
xi<-1:5
if (is.null(x)) x<-xi else x<-x+xi
}
cheers
Am 29.02.2024 um 09:23 schrieb Steven Yen:
Hello Eik:
Thanks. I do not need to sample. Essentially, I have a do loop which
produces 24 vectors of length of some length (say k=300) and 24 matrices
of 300x300. Then, I simply need to take the averages of these 24
vectors and matrices:
x=(x1+x2+...+x24)/k
y=(y1+y2+...+y24)/k
I am just looking for ways to do this in a do loop, which requires
initialization (to 0's) of x and y. My struggle is not knowning length
of x until x1 is produced in the first of the loop. Thanks.
Steven
On 2/28/2024 6:22 PM, Eik Vettorazzi wrote:
Hi Steven,
It's not entirely clear what you actually want to achieve in the end.
As soon as you "know" x1, and assuming that the different "xi" do not
differ in length in the real application, you know the length of the
target vector.
Instead of the loop, you can use 'Reduce' without having to initialize
a starting vector.
# generate sample vectors, put them in a list
xi<-lapply(1:5, \(x)sample(5))
# look at xi
xi
# sum over xi
Reduce("+",xi)
this works also for matrices
# generate sample matrices, put them in a list
Xi<-lapply(1:3, \(x)matrix(sample(16), nrow=4))
# look at them
Xi
# sum over Xi
Reduce("+",Xi)
Hope that helps
Eik
Am 28.02.2024 um 09:56 schrieb Steven Yen:
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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--
Eik Vettorazzi
Universitätsklinikum Hamburg-Eppendorf
Institut für Medizinische Biometrie und Epidemiologie
Christoph-Probst-Weg 1
4. Obergeschoss, Raum 04.1.021.1
20246 Hamburg
Telefon: +49 (0) 40 7410 - 58243
Fax: +49 (0) 40 7410 - 57790
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Vorstandsmitglieder: Prof. Dr. Christian Gerloff (Vorsitzender), Joachim Prölß,
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