Replace all but last instance of specified character

Question

If I have a string like

10,000kg crane,21

how should I strip all commas but the last to get

10000kg crane,21

I'm thinking this is a regular expression problem.

Answer 1

It can be done with regular expressions by using a lookahead assertion. You want to replace the commas that have at least one comma after them. The only comma for which this lookahead will fail is the last one.

Try this:

s = Regex.Replace(s, ",(?=.*?,)", "")

See it working online: ideone