Chart Plugin - How to handle the case where the value expression is not a number

Need help Plugins
1

I’m get data from an external API. The value is a string, and there is defined number of possible strings. I want to map the string to a number but I can’t seem to do it. For example I want to map Novice to 1 & Developing to 2
In the properties for the Line/Bar Chart, the only thing I can edit in the Value Expression is the current point.
I tried using find and replace but I could only define one replacement.
Any ideas anyone?