Swap all the values in a vector

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Vasilis Chasiotis 2020-4-12

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https://ww2.mathworks.cn/matlabcentral/answers/517295-swap-all-the-values-in-a-vector

评论： Thiago Henrique Gomes Lobato 2020-4-12

I have the vector x=[1 2 3 4 5 6 7 8] and I want to create another one in which I have swaped the elements as (17)(24)(38)(56), that is the new vector is [7 4 8 2 6 5 1 3].

Note that I have lots of vectors in which the number 1,...,8 are in different positions. So, I need to make a connection between the numbers, that is for example (17)(24)(38)(56), but not between the positions of the numbers in the vectors.

Is there any function in Matlab so as to achieve it?

Thanks!

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Answer 1

Thiago Henrique Gomes Lobato 2020-4-12

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https://ww2.mathworks.cn/matlabcentral/answers/517295-swap-all-the-values-in-a-vector#answer_425504

编辑：Thiago Henrique Gomes Lobato 2020-4-12

在 MATLAB Online 中打开

Yes, randperm:

rng(31415)
x=[ 1 2 3 4 5 6 7 8];
p = randperm(length(x));
xnew = x(p)
xnew =
     7     8     1     2     6     4     5     3

If you want only the specific case of your given permutation, you can do it by indexing and it looks like this:

xnew = x([7 4 8 2 6 5 1 3])
ans =
     7     4     8     2     6     5     1     3

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Vasilis Chasiotis 2020-4-12

编辑：Vasilis Chasiotis 2020-4-12

在 MATLAB Online 中打开

Your permutation is random, so it does not work.

For example in the vector x=[3 5 2 1 7 8 6 4], the desired output is [8 6 4 7 1 3 5 2].

So, I am asking about a function such that I connect numbers (17)(24)(38)(56) for each possible positions in the vectors.

Note that the numbers 1,...,8 are the elements of the vectors, not the positions of the vectors, and so

xnew = x([7 4 8 2 6 5 1 3])

does not work.

Thiago Henrique Gomes Lobato 2020-4-12

在 MATLAB Online 中打开

Sorry, I misunderstood your question. This code does what you want:

xref=[ 1 2 3 4 5 6 7 8];
x=[3 5 2 1 7 8 6 4];
[xsort,sortedIndex] = sort(x);
RightOrder = sortedIndex([7 4 8 2 6 5 1 3]); % Indexing in sorted array, so always the same
xnew = x;
xnew(RightOrder) = xref
x =
     8     6     4     7     1     3     5     2
     