Complicated recommendation model with multiple optional custom weighted attributes

### System information

- OS version/distro: Windows 11
- .NET Version: NET 6

### Issue

- **What did you try?**: tried to build a recommendation model with multiple optional custom weighted attributes
- **What happened?**: could not figure out how to apply custom attributes with weight
- **What did you expect?**: build a model with custom weighted attributes

### Use case
I would like to develop a recommendation system for cars (yes, vehicles), where user can specify what they are interested in most, less important and least important.

The importance would be described as:
- High: the weight value is 10
- Medium: the weight value is 6
- Low: the weight value is 3

And for every attribute of the car, a user is able specify the importance to them. Which means every attribute is optional. For those attributes that are not specified by the user, it would have default weight at `Medium`.

For example, a user specifies importance as below:
- price: high (more expensive, **lower** the score would be)
- horse power: high (bigger horse power, higher the score would be)
- seats: high (the system consider the number of seats as: the more the seats, the higher the score would be)
- 4WD: low (for those cars that are FWD/4WD, it has higher score)
- tank/fuel range: medium (longer the range, higher the score)
- etc.
- etc.

Now, to build such model, I would expect **somehow** we could provide user-specified weighted attributes into the model so the result would be user based.

Not really sure how to do so. Any thoughts?

Yours,
Wilson