Add space after commas only if it doesn't already?

Question

Is there a way to add a space after commas in a string only if it doesn\'t exist.

Example:

word word,word,word,

Would end up as

Answer 1

Using negative lookahead to check no space after comma, then replace with comma and space.

print 'word word,word,word,'.gsub(/,(?![ ])/, ', ')

Answer 2

If the string contains no multiple adjacent spaces (or should not contain such), you don't need a regex:

"word word, word, word,".gsub(',', ', ').squeeze(' ')
  #=> "word word, word, word, "

Answer 3

Add missing space:

 "word word,word,word,".gsub(/,(?=\w)/, ', ') # "word word, word, word,"

and removing the last unnecessary comma if necessary

"word word,word,word,".gsub(/,(?=\w)/, ', ').sub(/,\Z/, '') # "word word, word, word"

Answer 4

Just use a regular expression to replace all instances of "," not followed by a space with ", ".

str = "word word,word,word,"

str = str.gsub(/,([^ ])/, ', \1') # "word word, word, word,"