Select random elements from three consecutive columns in a big matrix?

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Hello all,
I have a 12 by 12 matrix, and I want to select 10 random elements. The elements should be from only three consecutive columns.
For example, I want to use 10 random elements from columns (1, 2, 3) or they could be from columns (2, 3, 4) or columns(3, 4, 5) and so on.
Any help please.
Thanks
  3 Comments
AM-Laurentian
AM-Laurentian on 5 Apr 2019
I am really sorry, it was a mistake. I realized that the question was submitted twice, I tried to delete it as soon as it was submitted but I could not. I apologies for any inconvenience.

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Answers (2)

Walter Roberson
Walter Roberson on 5 Apr 2019
N = 10;
[r, c] = size(YourMatrix);
start_col = randi([1, c-2]);
chosen = YourMatrix(start_col * r - 1 + randi([1 3*r], 1, N));

Jos (10584)
Jos (10584) on 5 Apr 2019
Edited: Jos (10584) on 5 Apr 2019
M = magic(5) % input data
N = 4 % number of selections
nC = 3 % number of consecutive columns
% engine
szM = size(M)
r = randi(szM(1), N, nC) % N x 3 random rows
c = randi(szM(2) - nC + 1, N, 1) % N random first columns
c = c + [0:nC-1] % add consecutive columns
R = M(sub2ind(szM, r, c)) % index into M

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