Replace new lines with a comma delimiter using Notepad++

Open the find and replace dialog (press CTRL+H).

Then select Regular expression in the ‘Search Mode’ section at the bottom.

In the Find what field enter this: [\r\n]+

In the Replace with: ,  -There is a space after the comma.

This will also replace lines like

Apples

Apricots
Pear

Avocados
Bananas

Where there are empty lines.

If your lines have trailing blank spaces you should remove those first. The simplest way to achieve this is

EDIT -> Blank Operations -> Trim Trailing Space

OR

TextFX -> TextFX Edit -> Trim trailing spaces

Be sure to set the Search Mode to “Regular expression”.