How to randomise scalars in a vector, in steps of 4?

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Bianca Elena Ivanof 2016-12-18

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回答： Star Strider 2016-12-19

counterbalancing.mat

Dear all,

I am trying to randomise the subconditions of the main conditions of my experiment (please see counterbalancing.mat attached). Column 2 of counterbalancing.mat contains speed levels (1, 2, 3) and column 3 sub-conditions (1, 2, 3, 4) for each speed level in column 3. What I am trying to do is, for every speed level (column 2), to randomise the 4 sub-conditions (column 3) - i.e. to randomise in steps of 4 - the first 4 rows containing 1, 2, 3, 4 and then the next 4 rows containing 1, 2, 3, 4 and so on and so forth, so that each and every speed level in column 2 has a different combination of 1, 2, 3 and 4's in column 3, if that makes sense.

I've tried using counterbalancing(1:4:408,3) but then it's dawned on me that this gives me a bunch of 1's because every row which is a multiple of 4 contains 1.......... I've then tried a for loop, but haven't been successful.

Could you please be so kind as to help me? Thank you very much in advance.

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Answer 1

Image Analyst 2016-12-18

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Try randperm() to scramble the positions of the 1-4 numbers for each subcondition.

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Bianca Elena Ivanof 2016-12-19

在 MATLAB Online 中打开

Hello,

Thank you for your response. I know randperm, I've tried it like this

scramble_subcond= counterbalancing(:,3);
counterbalancing(:,3)= scramble_subcond(randperm(numel(scramble_subcond)));

This does randomise it but it doesn't solve my issue - i.e. there will be speed levels in column 2 that only have subconditions 2, 2, 3, 3 in column 3, for example, whereas what I need is different combinations of all 1, 2, 3, and 4's per speed level.

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Answer 2

Star Strider 2016-12-19

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在 MATLAB Online 中打开

See if the perms function will do what you want:

Q = perms(1:4)
Q =
   3     2     1
   3     1     2
   2     3     1
   2     1     3
   1     3     2
   1     2     3
   4     2     1
   4     1     2
   2     4     1
   2     1     4
   1     4     2
   1     2     4
   4     3     1
   4     1     3
   3     4     1
   3     1     4
   1     4     3
   1     3     4
   4     3     2
   4     2     3
   3     4     2
   3     2     4
   2     4     3
   2     3     4