Many thanks for your replies and testing, but the target machine is running Perl 5.004 (unfortunately I wasn't precise enough when I just wrote Perl 5). The final solution was to use splice as suggested by jwkrahn in the next post.

In reply to Re^4: Add a fixed number of unique elements to hash [sample() vs. shuffle()] by Vasek
in thread Add a fixed number of unique elements to hash by Vasek

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