R 分层抽样

 library(sampling)

mtcars_order <- mtcars %>% arrange(gear)

mtcars_order %>% group_by(gear) %>% summarise(n=n())

smn <- round(prop.table(table(mtcars_order$gear))*10)

stratID <- strata(mtcars_order,stratanames='gear',size = smn,method = 'srswor')

head(stratID)

strat<-getdata(mtcars_order,stratID)

library(doBy)

mtcars %>% group_by(am,gear) %>% summarise(n=n())

mtcars %>% group_by(am) %>% summarise(n=n())

sampleBy(formula = ~ iris$Species,frac=0.1,data=iris)

sample_by(mtcars,formula = ~am+gear,frac = 0.2)