Generate Unique Sequence Numbers

Hello. I am looking for help to bring in unique sequence numbers to this file. I have an example attached. The sequence number should start with the vendor number, "-", and then have a sequence number starting at 1, within that vendor group. In the example you will see how I am trying to get the sequence numbers to come in and I am looking for something that could automate this for me. Right now, I am just sorting by vendor, and then running number series manually for each vendor, then doing a concatenate. Anything that would make this faster would be appreciated!

Thanks,