policyengine-aggregation

Use the adds property to sum variables across related entities like households or tax units. For simple aggregation, list source variables in adds without a formula. For conditional or transformed sums, write a formula() that calls add() with conditions, max_, or where logic to compute totals across entity members.

The adds property performs straightforward summation across entity members with minimal code. The add() function within a formula() enables complex logic: conditional sums, maximum values, filtered aggregation, and parameter-based calculations. Use adds for simple totals; use add() when you need conditions or transformations.

Yes. Define a final variable with adds listing income sources such as employment_income and self_employment_income. PolicyEngine automatically sums these across household members. For weighted or conditional income aggregation, use add() in a formula() to apply custom logic before summing.

Aggregation patterns support cross-entity summation: from SPMUnit to Household, or TaxUnit to SPMUnit. Use adds or add() to declare which entity members contribute to the total. The Skill handles automatic entity traversal; you specify the source variables and aggregation logic.

Yes. Use add() in a formula() to count qualifying members by applying boolean logic or where clauses. This enables counting dependents, summing only positive values, or aggregating based on entity attributes without writing custom iteration code.