[R] What don't I understand about sample()?

[Greg Snow]

Your call to `sample` does not specify the `size` or the number of
values to return, so it defaults to the same number in `x`, in this
case 10.  The `matrix` function then repeats the vector of 10 enough
times to fill in the matrix.

To do what you want you just need to specify the `size` as the total
number of values you want sampled, 50 or 5*10 for your case.

So the following should do what you want:

matrix(sample(1:10, 5*10, replace=TRUE), 5, 10, byrow=TRUE)

In this case the `byrow` does not really matter much since you are
just filling in random values.

Hope this helps,

On Thu, Mar 13, 2025 at 3:23 PM Kevin Zembower via R-help
<r-help using r-project.org> wrote:
>
> Hello, all,
>
> I'm learning to do randomized distributions in my Stats 101 class*. I
> thought I could do it with a call to sample() inside a matrix(), like:
>
> > matrix(sample(1:10, replace=TRUE), 5, 10, byrow=TRUE)
>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
> [1,]    8    2    3    1    8    2    8    8    9     8
> [2,]    8    2    3    1    8    2    8    8    9     8
> [3,]    8    2    3    1    8    2    8    8    9     8
> [4,]    8    2    3    1    8    2    8    8    9     8
> [5,]    8    2    3    1    8    2    8    8    9     8
> >
>
> Imagine my surprise to learn that all the rows were the same
> permutation. I thought each time sample() was called inside the matrix,
> it would generate a different permutation.
>
> I modeled this after the bootstrap sample techniques in
> https://pages.stat.wisc.edu/~larget/stat302/chap3.pdf. I don't
> understand why it works in bootstrap samples (with replace=TRUE), but
> not in randomized distributions (with replace=FALSE).
>
> Thanks for any insight you can share with me, and any suggestions for
> getting rows in a matrix with different permutations.
>
> -Kevin
>
> *No, this isn't a homework problem. We're using Lock5 as the text in
> class, along with its StatKey web application. I'm just trying to get
> more out of the class by also solving our problems using R, for which
> I'm not receiving any class credit.
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280 using gmail.com