[R] strange algorithm needed

[Gavin Simpson]

On Wed, 2006-11-01 at 09:36 -0500, Mark.Leeds at MorganStanley.com wrote:
> 
> i need a strange algorithm that i can easily do in a loop but need
> o do without looping.
> 
> suppose i have a vector of length y filled with zeros and a number x.
> 
> then, i want a new vector which is (1,......x,1......x,1.....x,1.....y mod
> x )
> 
> so if y was of length 17 and x was 3, the resultant vector should be
> 
> (1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2)
> 
> so basically , the algorithm should repeat seq(1,x) as many times as
> needed to fill y but
> then , if the last one doesn;'t fit perfectly, it should stop whenever it
> hits the end of y ?
> 
> rep(seq(1:x,length(y)/x) will work when there is a perfect fit but
> it can't handle the non fit cases. it just cuts
> off the non integer part of length(y)/x and then fills the vector
> do that the resultant vector is less than the length of y.

?rep, in particular the length.out argument. Using this, your desired
output is easily achieved:

> Y <- rep(0, 17)
> X <- 3
> Y <- rep(1:X, length.out = length(Y))
> Y
 [1] 1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 1 2
> yours <- c(1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2)
> all.equal(yours, Y)
[1] TRUE

HTH

G

> 
> thanks.
> 
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Gavin Simpson                     [t] +44 (0)20 7679 0522
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