Shuffle identical values of an array together

Hi,

Let us suppose arrays A and B:

A = [1 9 6 2 10 8 3 8 11 7 5 5 6]
B = [1 2 2 1 1  1 1 1 2  2 2 2 2]

I want to create an array C that randomly puts all element of array A with identical values in array B together (with out chanding the order of identical elements in array A). For example, the array C can be as follows:

C = [1 2 10 8 3 8 9 6 11 7 5 5 6]
C = [9 6 11 7 5 5 6 1 2 10 8 3 8]
% where the first group with identical values in B is [1 2 10 8 3 8] 
% and the second group is [9 6 11 7 5 5 6]

Now, let me clarify how the array C can be generated. First, I need to detect the uniqe values in the array B, which will be:

D = [1 2]

Then, I need to randomly sort the array D. Then, I will use the elements in sorted D to generate the array C as follows:

C = [A(B == D(1)) A(B == D(2))]

What would be the most efficient way for doing this action?

Many thanks for your attention, Amirhossein

[Jan]

I do not understand, how C is created. At first I thought, you want to shuffle the elements of A on the positions B==1, and in the next step at B==2, but this does not match the both examples C.

The first C can create by:

A = [1 9 6 2 10 8 3 8 11 7 5 5 6]
B = [1 2 2 1 1  1 1 1 2  2 2 2 2]
C = [A(B==1), A(B==2)]

But this is not random. So please explain again, what you exactly want.

[Amirhossein Moosavi]

Thanks for the question! Let me clarify by how the array C can be generated. First, I need to detect the uniqe values in the array B, which will be:

D = [1 2]

Then, I need to randomly sort the array D. Then, I will use the elements in sorted D to generate the array C as follows:

C = [A(B == D(1)) A(B == D(2))]

Is it clear now?

Answer 1

[Jan]

A = [1 9 6 2 10 8 3 8 11 7 5 5 6]
B = [1 2 2 1 1  1 1 1 2  2 2 2 2]

uB  = unique(B);
nuB = numel(uB);
uB  = uB(randperm(nuB));

C = [A(B == uB(1)), A(B == uB(2))];

I guess, that B can have an arbitrary number of elements. Then:

A = [1 9 6 2 10 8 3 8 11 13 7 5 5 6 14 15]
B = [1 2 2 1 1  1 1 1 2  3  2 2 2 2 3  3 ]

uB  = unique(B);
LUT = randperm(numel(uB));
BB  = LUT(B - min(B) + 1);
[~, index] = sort(BB);

D = A(index);