[RMP] Filtering

Problem:

In a production system customers need to filter out candidate recommendations for a variety of reasons.

Goal:

• Create a set of common filtering ops and a mechanism for executing them in systems.
• Determine if this can exist within NVTabular or whether it should be it's own unique library.

New Functionality

Systems

• Wrap as ops:
• Item attribute filtering op
• User attribute based selection of filter for item attribute filtering op
• Filter previous interactions op (bloom filter?)
• "Do not recommend from this list" filtering op (bloom filter? / item attribute flag)

##Docs/Examples

• Add filtering to existing end to end examples

Constraints:

• Access to item/user attributes, passed into this from the feature store or directly into the graph

Starting Point:

• interaction filters are commonly implemented as bloom filters
• item attribute filters are commonly implemented as queries with constraints