Generate a strata object from the data.
The function uses the POP_ID or STRATA columns along the
INDIVIDUALS.
generate_strata(data, pop.id = FALSE)A tidy dataset object.
Documented in tidy_genomic_data.
(logical) When pop.id = TRUE, the strata returns
the stratification colname POP_ID.
Default: pop.id = FALSE, returns STRATA.