I have a dataset of 10000 records which I want to use to compare two
prediction models.

I split the records into test dataset (size = ntest) and training dataset
(size = ntrain). Then I run the two models.

Now I want to shuffle the data and rerun the models. I want many shuffles.

I know that the following command

sample ((1:10000), ntrain)

can pick ntrain numbers from 1 to 10000. Then I just use these rows as the
training dataset.

But how can I make sure each run of sample  produce different results? I
want the data output be unique each time.
I tested sample(). and found it usually produce different combinations. But
can I control it some how? Is there a better way to write this?

Thank you,

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