@Varun-Teja ,
If it doesn’t matter which one you keep (that is, if it’s okay to keep only the last instance of a specific domain), then I would suggest doing it this way:
FIND = ((?-s)^.*?(https?://[^/]*/).*?$(\R|\Z))(?=(?s).*\2)
REPLACE = leave empty
SEARCH MODE = regular expression
3eb6a6e8-c5c8-47ca-9e2d-8ad11dbdcb4f-image.png
If it doesn’t matter what order they are in, then you could sort first (Edit > Line Operations > Sort Lexiocographically Ascending) and then use that replacement. (edit: Though that’s pointless, because just doing the first also is thus “doesn’t matter what order it’s in”)
If it does matter what order they are in, then you could use column-select (alt+click+drag) to select the zeroth column in the file, then use Edit > Column Editor > Number to Insert to insert numbers:
c54d34e2-89c3-4097-a432-00db12883acc-image.png
(You might want to do a second column select and then also insert a space between the numbers and the lines by selecting the zero-width column after the numbers and then typing a space)
1 https://www.fourthdomain.example/misc
2 https://www.fifthdomain.example/elsewhat
3 https://www.seconddomain.example/elsewhat
4 https://www.firstdomain.example/blah
5 https://www.seconddomain.example/blah
6 https://www.fourthdomain.example/blah
7 https://www.thirddomain.example/blah
8 https://www.firstdomain.example/elsewhat
Then, after that, sort descending (so in my example, it would be 8 down to 1). Then do the replacement I showed above. Then sort ascending again. Then remove the leading numbers (another column select followed by cut or backspace, or do a search-and-replace regular expression of FIND=^\d+\x20* and replace with nothing)