To get a random number

2012 1 18
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更新时间：2021 8 20
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Hi,
Am having a incremental column matrix like, e.g. for 1st iteration, it is 100*1(double), then for 2nd iteration iteration, it will be 100*2(double), etc.. Form this, for 1st iteration, i need to get a random no (single data only). from 1st column of matrix and for 2nd iteration, i have to get a random no. from 2nd column of matrix only.
Thank you in advance!!@!!

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Michael
Michael 2012-1-18
Maybe I misunderstand but to me this question appears contradictory. How is a number random if it depends on your column as an input?

回答（1 个）

Wayne King
Wayne King 2012-1-18

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You can use
x = randperm(100);
randomindex = x(1);
Then, use that index to choose an element from the appropriate column, say your data matrix is X
X(randomindex,1) %choose from first column
X(randomindex,2) %choose from 2nd column

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Hi wayne,
Am having negative integers also.
Wayne King
Wayne King 2012-1-18
How can you have negative indices in your vectors? that's not possible.
Hi wayne,
to get the vectors(i.e. 100*1,100*2), i used unifrnd command in the range b/w -0.8 to 0.2 for 100 populations. From this, i have to pick a data randomly.
Walter Roberson
Walter Roberson 2012-1-19
The range of your data matrix X does not affect the use of Wayne's suggested code.
However, to clarify his code a little:
rchoices = randperm(size(X,2));
randfirst = X(rchoices(1),1);
rchoices = randperm(size(X,2));
randsecond = X(rchoices(1),2);
Repeating the randperm() is required if you want it to be possible for the same row to be chosen for both columns. If the same row must _not_ be chosen for the columns, then
rchoices = randperm(size(X,2));
randfirst = X(rchoices(1),1);
randsecond = X(rchoices(2),2);
Hi walter,
It's not working.
am having both negative and non-negative integers of 100*1, In this i have to pick single data randomly.
Walter Roberson
Walter Roberson 2012-1-20
Sorry, the references to size(X,2) should have been size(X,1)
rchoices = randperm(size(X,1));
randchoice = X(rchoices(1),IterationNumber);
It's working...
Thanks walter

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