Kevin,
It is simple. Your matrix has fifty entries and you supplied just 10. R
tends to quietly assume you want the sample repeated as often as needed as
long as it can be used in whole amounts. So, you get five copies. If you
interchanged rows and columns with byrow=FALSE then every two rows would
repeat.
Ask for 50!
matrix(sample(1:50, replace=TRUE), 5, 10, byrow=TRUE)
But decide what you want. You are getting numbers in the range of 10. Asking
for 50 as I showed will get you something like this:
matrix(sample(1:50, replace=TRUE), 5, 10, byrow=TRUE)
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 15 32 20 4 44 20 34 2 30 14
[2,] 20 8 42 8 46 45 10 27 27 9
[3,] 26 12 15 26 8 47 25 31 38 31
[4,] 47 5 2 28 13 33 19 3 3 49
[5,] 12 1 11 3 12 21 1 19 30 31
What you may want is this with size=5*10
matrix(sample(x=1:10, size=5*10, replace=TRUE), 5, 10, byrow=TRUE)
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 2 1 9 9 3 5 7 4 4 10
[2,] 4 1 8 7 1 1 5 1 6 10
[3,] 4 3 6 2 4 4 10 10 8 8
[4,] 10 6 3 2 8 10 10 2 7 9
[5,] 2 4 2 5 5 10 10 10 8 1
-----Original Message-----
From: R-help <r-help-boun...@r-project.org> On Behalf Of Kevin Zembower via
R-help
Sent: Thursday, March 13, 2025 5:00 PM
To: r-help@r-project.org
Subject: [R] What don't I understand about sample()?
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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______________________________________________
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