Repeating a repeated sequence

Question

We want to get an array that looks like this:

1,1,1,2,2,2,3,3,3,4,4,4,1,1,1,2,2,2,3,3,3,4,4,4,1,1,1,2,2,2,3,3,3,4,4,4

What is the easiest way to do it?

it thought about a for loop, but isnt there a simpler way? – Fabian Stolz Jun 24 '12 at 18:35 — Fabian Stolz, Jun 24 '12 at 18:35

IRTFM · Accepted Answer · 2022-01-04T21:55:33.133

60

You can do it with a single rep call. The each and times parameters are evaluated sequentially with the each being done first.

rep(1:4, times=3, each=3)  # 'each' done first regardless of order of named parameters
#[1] 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4

edited Jan 04 '22 at 21:55

answered Jun 24 '12 at 21:20

IRTFM

258,963
21
364
487

score 20 · Answer 2 · answered Jun 24 '12 at 18:42

20

Or, simpler (assuming you mean a vector, not an array)

rep(rep(1:4,each=3),3)

answered Jun 24 '12 at 18:42

Dieter Menne

10,076
44
67

Looking at this years later, I'm not sure that it is simpler, but I think a case could be made that it is more flexible in that you could use it to perform the "times" operation first to be followed by "each" processing. – IRTFM Jan 04 '22 at 21:58

TheSciGuy · Answer 3 · 2019-03-06T22:20:06.490

9

42-'s answer will work if your sequence of numbers incrementally increases by 1. However, if you want to include a sequence of numbers that increase by a set interval (e.g. from 0 to 60 by 15) you can do this:

rep(seq(0,60,15), times = 3)
[1]  0 15 30 45 60  0 15 30 45 60  0 15 30 45 60

You just have to change the number of times you want this to repeat.

edited Mar 06 '19 at 22:20

answered Jun 20 '18 at 15:56

TheSciGuy

1,154
11
22

1

To further randomise the resulting vector (or change the order of the vector randomly), just do: sample(rep(seq(0,60,15), times = 3)) – Good Will Jun 01 '19 at 19:18

score 2 · Answer 4 · answered Jun 24 '12 at 18:39

2

Like this:

rep(sapply(1:4, function(x) {rep(x, 3)}), 3)

rep(x, N) returns a vector repeating x N times. sapply applies the given function to each element of the vector 1:4 separately, repeating each element 3 times consecutively.

answered Jun 24 '12 at 18:39

Stef Sijben

153
1
8

3

You should take a look at Dieter's answer - the 'each' parameter would do what you're doing a lot nicer than using a call to sapply. – Dason Jun 24 '12 at 19:45

score 0 · Answer 5 · answered Nov 01 '17 at 20:20

Here is a method using array manipulation with aperm. The idea is to construct an array containing the values. Rearrange them so they match the desired output using aperm, and then "unfold" the array with c.

c(aperm(array(1:4, dim=c(4,3,3)), c(2, 1, 3)))
 [1] 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4 1 1 1 2 2 2 3 3 3 4 4 4

Repeating a repeated sequence

5 Answers5

Linked