This helper function returns the list of stratification variables used
to generate a `signals_agg` object. If no stratification was applied
(i.e., all values in the `category` column are `NA`), it returns `NULL`.
Usage
get_strata_from_signals_agg(signals_agg)
Arguments
- signals_agg
A data frame containing precomputed signal aggregations, produced by [aggregate_signals()].
Must include a `category` column that encodes the stratification variable(s).
Value
A character vector of stratification values (e.g., `"age_group"`, `"county"`),
or `NULL` if no stratification was applied.