Add utility function to simplify multi-table schemas

[frances-h]

Problem Description

Currently, HMA cannot run on certain multi-table schemas. We issue a warning when a schema will generate too many columns, and we should provide a utility function to easily reduce a multi-table schema so it can successfully run on HMA.

Expected behavior

Add a new utility function utils.simplify_schema:
Parameters:

• data - the data dictionary
• metadata - the MultiTableMetadata for this dataset

Returns:

• A data dictionary mapping table names to simplified tables
• MultiTableMetadata for the simplified data schema

from sdv.utils import simplify_schema

simple_data, simple_metadata = simplify_schema(
  data=my_data,
  metadata=my_metadata
)

Algorithm overview

For every root table:

• drop any table that is depth > 2 away from the parent (i.e. keep only direct children and grandchildren) and count the number of tables connected to the root

Select the root with the greatest number of descendant tables
Calculate the number of extended columns we can add to the root (we can reuse the logic used to generate the warning in HMA)
Allocate a # of augmented columns to each child relationship
For each child:

• Determine the number of modelable columns and add the number of child relationships for that child
• If the number of modelable columns will generate more than the allowed number of extended columns, drop modelable columns from the child
  • Try to keep a variety of sdtypes
  • If we cannot drop columns so that we will not exceed the maximum number of extended_columns, drop any grandchild tables until we can

For each grandchild:

• Drop all modelable columns (grandchildren should only generate a num_rows column in their parents)

Additional context

We should also change the warning in HMA to point to this utility function:

>>> synthesizer = HMASynthesizer(metadata)
PerformanceAlert: Using the HMASynthesizer on this metadata schema is not recommended because HMA will generate a large number of columns

Table Name   # Columns in Metadata   Est # Columns
users        12                      123123123
transactions   
...

We recommend simplifying your metadata schema using utils.simplify_schema