A note on sampling a tape-file

The problem of selecting a random sample of precisely n records from a tape film containing N records sometimes arises in data processing applications. If a means of obtaining a random sample of n integers r1, r2, … ,rn selected from the N integers 1, 2, … , N is available, the problem is theoretically simple. All that need be done is to then select the r1th, r2th, … , rnth records.