# NOT RUN {
library(survey)
data(api)
dstrata <- apistrat %>%
as_survey_design(strata = stype, weights = pw)
dstrata_grp <- dstrata %>%
group_by(stype)
dstrata_grp %>%
cascade(api99 = survey_mean(api99),
api00 = survey_mean(api00),
api_diff = survey_mean(api00 - api99))
# }
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