I would like to clarify exactly what you are thinking.
Currently "Remove Duplicate Lines, (ordered|sorted)" keeps the *first* occurrence of a repeating line.
The function you are suggesting would remove *all* occurrences of a repeating line?
Example | File | Result --- | --- | --- ex.1 | cat<br>**dog**<br>cat<br>cat<br>cat<br>**tree** | **dog**<br>**tree** ex.2 | cat<br>**dog**<br>cat<br>tree<br>cat<br>cat<br>tree | **dog**
<sub><sup>* no animals where harmed in the creation of this table</sup></sub>