我可以获得由其他变量分层的变量的摘要，如下所示：
require(data.table)
DT <- data.table(mtcars)
var_work <- "hp"
by_vars <- c("cyl", "carb")
ans_1 <- cube(DT, j = as.list(quantile(get(var_work))), by = by_vars)
ans_1
cyl carb 0% 25% 50% 75% 100%
1: 6 4 110 110.00 116.5 123.00 123
2: 4 1 65 66.00 66.0 93.00 97
3: 6 1 105 106.25 107.5 108.75 110
4: 8 2 150 150.00 162.5 175.00 175
5: 8 4 205 218.75 237.5 245.00 264
6: 4 2 52 69.25 93.0 105.50 113
7: 8 3 …