Random shuffle of vector elements

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

Answer 1

[Constantino Carlos Reyes-Aldasoro]

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.

Hope this solves your question.

Answer 2

[Fangjun Jiang]

p=randperm(3);
index=[1,1+p,5];
b=A(index);

[Fangjun Jiang]

do it in one shot

p=perms(2:4);
index=[ones(6,1), p, 5*ones(6,1)];
b=A(index)