This can be overcome by additional steps in the process. However the caveat is that now the file will have accounts in possibly a different order to what they were initially before combining and sorting. Also remove the appended b to clean up those lines. This can be completed in either 1 or 2 regexes.

Use a regular expression (regex) to remove all lines with the a appended or a b line where there is no corresponding a line.Thus an account with “a” would appear before the corresponding line from file #2 (which has a b appended to account number). For the file with other additional information append a b to the account number and if required copy that account number (with b) to the front of the line.For the file with ONLY account numbers, append an a to the account number.I don’t use plugins, of which there are quite a few, and maybe one of those might have what you are looking for.

I need to match file one to file two and delete the non-matching lines How do you compare two Dataframes and get the difference?.How do I check if two CSV files are the same in Python?.Can we compare two files in Notepad ++?.What do the colors mean in Notepad ++ compare?.

Compare in notepad++