how to choose matrix columns randomly?

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maryam 2015-2-23

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评论： Star Strider 2015-2-23

hi all. i have two related matrices (A and B). i want to choose randomly 80% of one matrix's columns (e.g A) and corresponding values from second matrix(B)for example:

suppose that two matrices are like this:

A=[1 2 3 4 5 6 7 8 9 10];
B=[11 12 13 14 15 16 17 18 19 20];

desired matrices are for example like:

C=[1 3 4 5 7 8 9 10]
D=[11 13 14 15 17 18 19 20]

would you help me on this? thank you

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the cyclist 2015-2-23

编辑：the cyclist 2015-2-23

Do you want the 160 to be unique, or possibly repeating? For example, might you choose the 5th column twice?

Also, do you have the Statistics Toolbox? A couple commands there make this a bit cleaner.

maryam 2015-2-23

no, columns should be unique. yes, i have statistics toolbox,but i haven't work with it yet!

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Answer 1

Star Strider 2015-2-23

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在 MATLAB Online 中打开

Use the randperm function.

This might do what you want:

cols = randperm(200, 160);

(Note: Untested code, but it should work.)

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maryam 2015-2-23

thank you for your answer

Star Strider 2015-2-23

My pleasure!

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Answer 2

the cyclist 2015-2-23

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As Stephen's questions suggest, you need some more specification.

Possible elements of the solution are

randi, randsample, or other commands to select some random indices. (Say that vector of random indices is called idx )
Something like either B(:,idx) or B(:,A(idx)) to choose from B directly with the indices, or using values from A that are selected by the indices

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the cyclist 2015-2-23

在 MATLAB Online 中打开

idx = randsample(200,160);
C = A(idx);
D = B(idx)'

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Answer 3

Jos (10584) 2015-2-23

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在 MATLAB Online 中打开

Exactly 80 vs 20? Or in approximation? And how many columns? I also assume the number of rows in A and B are the same.

A suggestion is that you first draw N columns from A and M columns from B, where N/M is 80/20

Ntotal = 10 ;
N = ceil(.8 * Ntotal) % fixed 80 vs 20
% or
% N = sum(rand(100,1)<0.8)) % roughly
M = Ntotal - N 
% select N columns from A and M columns from B
cidxA = randi([1 size(A,2)],1,N)
cidxB = randi([1 size(B,2)],1,M)
% stick them together
OUT = [A(:,cidxA) B(:,cidxB)]
% randomise the order
r = randperm(size(OUT,2))
OUT = OUT(:,r)