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

1 view (last 30 days)
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
Guillaume
Guillaume on 5 Apr 2019
Edited: Guillaume on 5 Apr 2019
Please do not ask the same question twice.
And it looks like you delete your question once answered, which is not going to go down well with us (and will be restored anyway).
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.

Sign in to comment.

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

Categories

Find more on Creating and Concatenating Matrices in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!