这么慢的原因是因为你正在调用你的函数length(e)
时间。它对小向量并没有太大的区别,但是 R 函数调用的开销确实开始与更大的向量相加。
通常,您需要将其移动到已编译的代码中,但幸运的是您可以使用findInterval
:
set.seed(21)
e <- rnorm(1e4)
g <- rnorm(1e4)
O <- findInterval(e,sort(g))/length(g)
# Now for some timings:
f <- function(p,v) mean(v<=p)
system.time(o <- sapply(e, f, g))
# user system elapsed
# 0.95 0.03 0.98
system.time(O <- findInterval(e,sort(g))/length(g))
# user system elapsed
# 0 0 0
identical(o,O) # may be FALSE
all.equal(o,O) # should be TRUE
# How fast is this on large vectors?
set.seed(21)
e <- rnorm(1e7)
g <- rnorm(1e7)
system.time(O <- findInterval(e,sort(g))/length(g))
# user system elapsed
# 22.08 0.08 22.31