I think you may want to change the order of those statements since weird things could happen as it is now.

Since you're first taking out digits and underscores, you might be artificially creating a 'csr' phrase. Take 'doc09_srt_whatever', do you want it to end up as 'dotwhatever'?

Of course this may never happen with your specific data (now?), but it's something to keep in mind.

Hope this helps, -gjb-