Question

I am using a regex to find dupliates in a list. It is only a short comma seperated list, and performance is not an issue, so there is no need to tell me I should not use regex for those reasons.

// returns a match because some is repeated
"some,thing,here,some,whatever".match(/(^|,)(.+?)(,|,.+,)\2(,|$)/g)

Questions…

1. Can this regex be improved?
2. Does it cover all possible scenarios where comma is not in the seperated strings
3. Is there a better (preferably more readable and more efficient) way to do this?

Answer 1

I don’t see the purpose of using regexes here, unless you like unimaginable pain. If I had to find duplicates I would

• Obtain an array of words

  var words = "...".split(',');
  

• optionally lowercase everything, if you feel like doing that

• sort the array

  words.sort()
  

• Duplicates should now all be in consecutive positions of the array.

As an extra advantage, I`m pretty sure this would be vastly more efficient than a regex version.