CODEWITHSUNDEEP
arraysmatlabrandom
user36610
user36610

Reputation: 45

Choose one element in arrays

I have N groups of arrays. Each group contains 3 arrays for example. Now I would like to take only one array from each of these groups and take a product with B array.

For example:

B_1(:,:,m)=C_1, where m is size( B_i, 3)

In each B_i there are 8 sub-array C_k. I am looking for an algorithm that helps me to take random one of them (one of C_k) and use it later for another computation.

How can I implement random choosing of the array in B_i?

Upvotes: 1

Views: 299

Answers (1)

Adriaan
Adriaan

Reputation: 18177

You want a random column, with index 1, 2, 3. Thus, don't set numel(A) as your max integer in randi(), instead, set it at 3:

A = rand(2,2,3,5); % three 2-by-2 matrices, in each of 5 groups
B = rand(2,2); % Chosen for convenience; replace as warranted

% Preallocate C to have the same size as A_k * B, with as many groups
C = zeros([size(A,1),size(A,2),size(A,4)]);

for ii=1:size(A,4)  % Loop over all groups/slices
    % Choose a random column in {1, 2, 3} for each slice ii
    C(:,:,ii) = A(:,:,randi(3),ii)*B;
end

In this example there are 5 groups (fourth dimension of A), each group has three entries (third dimension), of 2 -by- 2 matrices (first two dimensions). Thus, loop over each group, the fourth dimension, choose a random A matrix through randi(3) on the third dimension, then multiply the remaining two dimensions with B, and store in C. C will have the dimensions of A_k * B, in this case chosen to be 2 -by- 2, and as third dimension the number of groups in A.

Upvotes: 1

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