Cleaning a Feed You Did Not Write

One reported assessment problem is simply a data file with duplicates and corrupted records in it, and instructions to produce a clean one. Candidates who treat it as an exercise in string handling do badly. It is an exercise in deciding what to do with input that is wrong, which is a design question with no single right answer and several clearly wrong ones.

The four failures, in the order they arrive

Duplicates. The same logical record twice. Sometimes byte-identical, which is easy, and sometimes the same event with a different arrival timestamp, which is not. The question to answer first is what makes two records the same, and the answer is a key drawn from the fields the sender controls, never from the fields your own pipeline stamped on.

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