Javascript Or Notepad++ Regular Expression To Add Thousands Separator To Arbitrary Text

As part of a visualisation, I'd like to add thousands separators to any numbers (contiguous string of digits) in a string. It needn't consider the context of the number e.g. 1234e+

Solution 1:

It's pretty much the same as your attempt, just reversed and with a quantifier:

\d(?=(?:\d{3})+(?!\d))

And replace that with $&,.

The (?:\d{3})+ makes sure that there is a multiple of 3 digits following and the (?!\d) then makes sure that there is no fourth or fifth digit following.

If you want to use this in Notepad++ make sure to upgrade to version 6.

Note that in Notepad++ you could also use a lookbehind:

(?<=\d)(?=(?:\d{3})+(?!\d))

And replace that with ,.

Solution 2:

You could use this expression:

((?<=\d)\d{3}(?=\D|(?:\d{3})*(?:\D|$)))

And replace by ,$1.

The lookbehind makes sure there's a number before the 3 digits we're matching.

The 3 digits we're matching are the 'thousands' you want to put a comma before.

The lookahead makes sure there's either a non-digit after, or a set of triplets of digits.