Choose one array for each group of arrays?

[poster]

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

For example:

Group_1=[A_1 ,A_2, A_3];

...

Group_N=[A_m ,A_k, A_l];

Now I am choosing one array in each group and taking a product with B

C_1=A_2*B;  % Matlab has choosen random A_2 in group_1



...



C_N=A_k*B;  % Matlab has choosen random A_kin group_N

How to implement such computation?

I have tried A(randi(numel(A))), but it doesn't work.

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