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matrix with different randperm rows

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Jeremy
Jeremy am 17 Sep. 2014
Kommentiert: Jeremy am 18 Sep. 2014
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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Andrei Bobrov
Andrei Bobrov am 17 Sep. 2014
Bearbeitet: Andrei Bobrov am 17 Sep. 2014
[~, out] = sort(rand(M,N),2);
  3 Kommentare
Mikhail
Mikhail am 18 Sep. 2014
Apparently, not-))
Jeremy
Jeremy am 18 Sep. 2014
Works orders of magnitude faster for large group sizes :)

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Weitere Antworten (3)

Guillaume
Guillaume am 17 Sep. 2014
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

Mikhail
Mikhail am 17 Sep. 2014
  4 Kommentare
Image Analyst
Image Analyst am 17 Sep. 2014
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
Jeremy am 17 Sep. 2014
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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Joseph Cheng
Joseph Cheng am 17 Sep. 2014
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.
  1 Kommentar
Joseph Cheng
Joseph Cheng am 17 Sep. 2014
Bearbeitet: Joseph Cheng am 17 Sep. 2014
ok well it is possible to do it without a loop in 2ish lines. Use the function arrayfun() or cellfun() on an array of N*ones(M,1).

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