R help - Jun 2008 - How to run coxph() with time dependent cohort sampling

Now that we have case cohort model , we have 1000 people and 50 cases

   Let the first       10 cases occur at the same time
        second     10         "
        third       10         "
        fourth       10        "
        fifth        10        "

 How easy is it to randomly sample 50 different
 cohort controls for each group?

That is:

randomly sample 50 cohort controls for the first 10 cases from all 1,000

randomly sample 50 new cohort controls for the second 10 cases from the
 surviving 990

randomly sample 50 new cohort controls for the third 10 cases from the
 surviving 980

randomly sample 50 new cohort controls for the fourth 10 cases from the
 surviving 970

randomly sample 50 new cohort controls for the fourth 10 cases from the
 surviving 960

and run these through a time dependent COX-PH?

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