How to select a random sample without replacement with imposed condition?

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Hi,

I'd like to draw a random sample from my population. My population is a vector x of size (N x 1). My sample should satisfy

sum(x(sample)) = 0.7*sum(x);

So I do not care how many observations I draw from the sample, but I just want to make sure that the resulting sample covers 70 percent of total x in terms of value, not in terms of number.

Thanks, Christian

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Walter Roberson 2015-10-24

Is that exactly 0.7 ? If so then it might not be possible to satisfy the condition.

Christian 2015-10-24

Good point. Let's say at least 0.7, but as close as possible to 0.7. So stop sampling as soon as the sum is equal or greater than 0.7.

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Answer 1

Walter Roberson 2015-10-24

在 MATLAB Online 中打开

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rp = randperm(N);
loc = find( cumsum(x(rp)) >= 0.7 * sum(x), 1, 'first');
samps = x(rp(1:loc));

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Christian 2015-10-24

Thanks. Very neat.

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