I have a vector from 1 to 40 and want to shuffle it in such a way that each block of four integers (ten blocks in total) are shuffled only with themselves.
For example: 3 4 2 1 | 7 6 5 8 | 9 11 10 12 | ...
My original idea was to append ten permutation vectors to eachother and then add a 1 to 40 vector to the big permutation vector, but it didn't work at all as expected and was logically wrong.
Has anyone an idea how to solve this?
data = 10:10:120; % input: values to be permuted
group_size = 4; % input: group size
D = reshape(data, group_size, []); % step 1
[~, ind] = sort(rand(size(D)), 1); % step 2
result = D(bsxfun(@plus, ind, (0:size(D,2)-1)*group_size)); % step 3
result = result(:).'; % step 4
Example result:
result =
20 10 30 40 60 50 70 80 110 100 120 90
D
, such that each group is a column. This is done with reshape
.ind
, where each column contains the indices of a permutation of the corresponding column of D
. This is done generating independent, uniform random values (rand
), sorting each column, and getting the indices of the sorting (second output of sort
).ind
as column indices into D
. This requires converting to linear indices, which can be done with bsxfun
(or with sub2ind
, but that's usually slower).