[R] Random sampling while keeping distribution of nearest ne

[(Ted Harding)]

On 12-Aug-09 22:05:24, Emmanuel Levy wrote:
> Dear All,
> I cannot find a solution to the following problem although I imagine
> that it is a classic, hence my email.
> 
> I have a vector V of X values comprised between 1 and N.
> 
> I would like to get random samples of X values also comprised between
> 1 and N, but the important point is:
> * I would like to keep the same distribution of distances between the X
> values *
> 
> For example let's say N=10 and I have V = c(3,4,5,6)
> then the random values could be 1,2,3,4 or 2,3,4,5 or 3,4,5,6, or
> 4,5,6,7 etc..
> so that the distribution of distances (3 <-> 4, 3 <->5, 3 <-> 6, 4 <->
> 5, 4 <-> 6 etc ...) is kept constant.
> 
> I couldn't find a package that help me with this, but it looks like it
> should be a classic problem so there should be something!
> 
> Many thanks in advance for any help or hint you could provide,
> All the best,
> Emmanuel

If I've understood you right, you are basically putting a sequence
with given spacings in a random position amongst the available
positions. In your example, you would randomly choose between
1,2,3,4/2,3,4,5/3,4,5,6/4,5,6,7/5,6,7,8/6,7,8,9/7,8,9,10/

Hence a result Y could be:

  A <- min(V)
  L <- max(V) - A + 1
  M <- (0:(N-L))
  Y <- 1 + (V-A) + sample(M,1)

I think this does it!

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
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Date: 12-Aug-09                                       Time: 23:49:22
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