At a guess, this is a language barrier issue. He is removing the "duplicateness" by adding a tag which makes each line unique; in a sense, that is "removing duplicates" -- though this isn't the phrase a native English speaker would likely use to describe the process. Gotta' make room for the human factor here; some tolerance in language parsing can be healthy.

In reply to Re^2: To remove duplicate lines and add digits as per loop by marinersk
in thread To remove duplicate lines and add digits as per loop by suvendra123

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