# Random shuffle of vector elements

9 views (last 30 days)
Premysl Stastny on 5 Oct 2021
Commented: Fangjun Jiang on 5 Oct 2021
Hello,
How to randomly shuffle all elements of the vector except the first and last position?
For example:
I have vector A=[5 1.5 1.6 1.7 5] and I want to randomly shuffle 2nd, 3rd 4th element while the 1st and the last will stay the same.
Thank you

This can be easily done by addressing the vector correctly. First you need a random order to shuffle your elements. You can do that by using rand and then sort:
[a,b]=sort(rand(1,3))
a = 1×3
0.0591 0.2095 0.2737
b = 1×3
3 2 1
so b will be the order. Now you need to use that to re-order your vector, let's call the new vector A2:
A=[5 1.5 1.6 1.7 5];
A2 = [A(1) A(b+1) A(end)]
A2 = 1×5
5.0000 1.7000 1.6000 1.5000 5.0000
Now you have a new vector with the first and last same as they were, but 2:4 have been randomly shuffled.

Fangjun Jiang on 5 Oct 2021
p=randperm(3);
index=[1,1+p,5];
b=A(index);
Fangjun Jiang on 5 Oct 2021
do it in one shot
p=perms(2:4);
index=[ones(6,1), p, 5*ones(6,1)];
b=A(index)

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