我从下面的表dt
开始,尝试按列表keys
对其列进行子集化:
library(data.table)
set.seed(123)
randomchar <- function(n, w){
chararray <- replicate(w, sample(c(letters, LETTERS), n, replace = TRUE))
apply(chararray, 1, paste0, collapse = "")
}
dt <- data.table(x = randomchar(1000, 3),
y = randomchar(1000, 3),
z = randomchar(1000, 3),
key = c("x", "y", "z"))
keys <- with(dt, list(x = sample(x, 501),
y = sample(y, 500),
z = sample(z, 721)))
我可以通过循环获得我想要的结果:
desired <- copy(dt)
for(i in seq_along(keys)){
keyname <- names(keys)[i]
desired <- desired[get(keyname) %in% keys[[i]]]
}
desired
问题是 - 是否有更多data.table惯用方法来执行此子集?
我尝试使用CJ
:dt[CJ(keys)]
,但这需要很长时间。
答案 0 :(得分:4)
如何在此蒙版上构建蒙版并过滤dt
:
dt[Reduce(`&`, Map(function(key, col) col %in% key, keys, dt)),]