在R中对seq进行矢量化的表达和有效方法是什么？

Question

I am aware of seq, which used in this way:

seq(by=1, to=3, by=1)

will get you from c(1) to

c(1,2,3)

How can I vectorize this behavior to go from

Input:

c(1,1,1)

Output:

 c(1,1,1,2,2,2,3,3,3)

Answer 1

seq isn't vectorised. You could use one of the loops to get the same behavior.

For example, with mapply

x <- c(1,1,1)
c(t(mapply(seq, x, 3)))
#[1] 1 1 1 2 2 2 3 3 3

If you want every sequence go till length(x) use that instead of hard-coded 3.

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Besides, if your x will always start with 1 as shown in the example you can use rep and sequence

sort(sequence(rep(length(x), length(x))))
#[1] 1 1 1 2 2 2 3 3 3

Answer 2

An option is rep and it is vectorized. No need to use loops

rep(seq_along(v1), each = length(v1))
#[1] 1 1 1 2 2 2 3 3 3

---

Or another option is replicate

c(t(replicate(3, seq(1, 3, 1))))
#[1] 1 1 1 2 2 2 3 3 3

---

If we wanted to vectorize the seq , use Vectorize

c(t(Vectorize(function(x) seq(x, 3, 1))(v1)))
#[1] 1 1 1 2 2 2 3 3 3

data

v1 <- c(1, 1, 1)