install.packages("sampling")
library(sampling)
install.packages("data.table")
library(data.table)

set.seed(1)
N <- 1e4
d <- data.table(fasciaEta = sample(1:5, N, T), 
                sesso = rbinom(N, 1 , .5),
                spesaMensile = rnorm(N, 100, 6.7))

# Sort
setkey(d, fasciaEta, sesso)

# Population size by strata
d[, .N, keyby = list(fasciaEta, sesso)]

# Select sample
set.seed(2)
s <- data.table(strata(d, c("fasciaEta", "sesso"), size=rep(30, 10), "srswor"))

?strata

dim(s)

# Sample size by strata
s[, .N, keyby = list(fasciaEta, sesso)]


s <- data.table(strata(d, c("fasciaEta", "sesso"), size = round(c(967/n*300, 958/n*300, 1116/n*300, 928/n*300, 1026/n*300, 984/n*300, 1025/n*300, 1027/n*300, 1007/n*300, 962/n*300)),"srswor"))