5000 hash entries of a four digit key won't be a problem for any computer built in this century.

You don't need a regex. Sure, you can use one, but my split accomplishes the same thing more clearly, in my opinion. I just split on ',' and then select the first element of the split. That isolates your index number.

My solution ought to work as long as your data set matches your description, and as long as I didn't inadvertently impose some typos into my code. ;)