Remove all white space in a file and replace them with a comma using Vim

Another way to do it :

%s/\s\{1,}/,/gc

First delete the blank lines:

:g/^\s*$/d

Then use a substitution (:s///) over each line (%) to replace all (g) continuous whitespace (\s\+) with a comma (,).

 :%s/\s\+/,/g