repeating values in an index two by two

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Iakub Henschen
Sent: Monday, November 11, 2013 8:42 AM
To: r-help at r-project.org
Subject: Re: [R] repeating values in an index two by two

n<-7
rep(seq(1,n,2), each=4)+c(0,1,0,1)

 [1] 1 2 1 2 3 4 3 4 5 6 5 6 7 8 7 8

rep(), seq(), rbind(), apply() ... whatever: internally there will always
be iteration via some loop :-)

Ia.


On Mon, Nov 11, 2013 at 11:16 AM, Carl Witthoft <carl at witthoft.com> wrote:

Here's a rather extreme solution:

 foo<-rep(1:6,each=2)
Rgames> foo
 [1] 1 1 2 2 3 3 4 4 5 5 6 6

Rgames> foo[rep(c(1,3,2,4),3)+rep(c(0,4,8),each=4)]
 [1] 1 2 1 2 3 4 3 4 5 6 5 6

In the general case, then, it would be something like

foo<- rep(1:N, each = 2)  # foo is of length(2*N)

foo[rep(c(1,3,2,4),2*N/4 + rep( seq(0, 3*N/4,by=4),each=4)]

Note that the refolding requires the sequence to have length a multiple of
4.




Patrick Burns wrote

f1

function(x) {
     one <- matrix(1:x, nrow=2)
     as.vector(rbind(one, one))
}
<environment: 0x000000000daaf1c0>

 > f1(8)

  [1] 1 2 1 2 3 4 3 4 5 6 5 6 7 8 7 8

Pat


On 11/11/2013 12:11, Federico Calboli wrote:

Hi All,

I am trying to create an index that returns something like

1,2,1,2,3,4,3,4,5,6,5,6,7,8,7,8

and so on and so forth until a predetermined value (which is obviously
even).  I am trying very hard to avoid for loops or for loops front

ends.

I'd be obliged if anybody could offer a suggestion.

BW

F

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