matrix with different randperm rows

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Jeremy 2014-9-17

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评论： Jeremy 2014-9-18

Hi,

Say I have vector of N integers, 1 through N. Is there a quick way, without loops, to create a matrix where each row is a different randperm of the vector? My N can get large (up to 100).

Thanks

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Answer 1

Andrei Bobrov 2014-9-17

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编辑：Andrei Bobrov 2014-9-17

在 MATLAB Online 中打开

[~, out] = sort(rand(M,N),2);

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Mikhail 2014-9-18

Apparently, not-))

Jeremy 2014-9-18

Works orders of magnitude faster for large group sizes :)

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Answer 2

Guillaume 2014-9-17

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在 MATLAB Online 中打开

cell2mat(arrayfun(@(dummy) randperm(n), 1:m, 'UniformOutput', false)');

Whether or not that can be said to be without a loop is debatable as arrayfun is effectively looping over the array 1:m

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Answer 3

Mikhail 2014-9-17

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Yes, try http://www.mathworks.com/help/matlab/ref/perms.html

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Image Analyst 2014-9-17

In what universe, or decade, is 100 considered large? You actually mean 100, right, like ten times ten, not 100 million or 100 billion or something?

Jeremy 2014-9-17

100 is large when you talk about some types of group coordination. I need to select k individuals from a group of N to interact at different time steps. What I've been doing is generating all combinations and randomly selecting ones to fill an interaction matrix, but that combination matrix gets big fast.

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Answer 4

Joseph Cheng 2014-9-17

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Well there is a randperm() function that will give you a random permuation. How to get it as a MxN matrix without a loop will take some more time to think about it.