how to select random rows from a matrix?

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N 2011-10-7

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编辑： Walter Roberson 2024-3-10

i have a matrix of size 10037 by 9.

please tell me how to select 1000 random rows from the matrix and save it as a mnew matrix in another variable.

thanks in advance.

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回答（2 个）

Andrei Bobrov 2011-10-7

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m = rand(10037,9);
k = randperm(10037);
mnew = m(k(1:1000),:);

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Jan 2017-10-24

在 MATLAB Online 中打开

Or with the original order:

M = rand(10037,9);
k = randperm(10037, 1000);
Selected  = M(k, :);
r         = true(1,10037);
r(k)      = false;
Remaining = M(r, :);

Alejandro Reyes 2024-3-10

This works. Thank you!

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Richard Willey 2011-10-7

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Statistics Toolbox includes a nice function called randsample

% Generate a matrix named foo
foo = randn(10000,2);
% draw 1000 random samples without replacement
index = randsample(1:length(foo), 1000);
bar = foo(index,:);
% draw 1000 random samples with replacement
index = randsample(1:length(foo), 1000, true);
bar = foo(index,:);

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Peter Perkins 2011-10-7

If you happen to be using R2011b, and have access to the Statistics Toolbox, you can also use the new datasample function:

m = rand(10037,9);

mnew = datasample(m,1000);

This also allows you to sample with replacement, or with weights.

Ege 2015-1-4

编辑：Ege 2015-1-4

And when we selected 1000 of them, how do we delete the selected rows from the original matrix which in this case foo ? And what does replacement mean in here?

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