[R] Dequantizing

roger koenker rkoenker at uiuc.edu
Thu Nov 20 18:31:43 CET 2008

I'm rather doubtful that you can improve on the uniform  jittering  
you originally considered.  It would require intimate knowledge about
the non-uniformity of the density in the spacings between your  
quantized version.
But if you really _knew_ the parent distribution
then something like the following might have been what you had
in mind:

# Toy dequantization example
rate <- 1
x <- sort(rexp(100,rate))
xu <- x + runif(100)
y <- floor(x)
ty <- table(y)
p <- c(0,cumsum(table(y)/length(y)))
pup <- p[-1]
plo <- p[-length(p)]
fun <- function(ty,plo,pup) qexp(runif(ty,plo,pup),rate)
z <- unlist(mapply(fun, ty = ty, plo = plo, pup = pup))

url:    www.econ.uiuc.edu/~roger            Roger Koenker
email    rkoenker at uiuc.edu            Department of Economics
vox:     217-333-4558                University of Illinois
fax:       217-244-6678                Champaign, IL 61820

On Nov 20, 2008, at 9:43 AM, Stavros Macrakis wrote:

> I have some data measured with a coarsely-quantized clock.  Let's say
> the real data are
>      q<- sort(rexp(100,.5))
> The quantized form is floor(q), so a simple quantile plot of one
> against the other can be calculated using:
>      plot(q,type="l"); points(floor(q),col="red")
> which of course shows the characteristic stair-step.  I would like to
> smooth the quantized form back into an approximation of the underlying
> data.
> The simplest approach I can think of adds a uniform random variable of
> the size of the quantization:
>      plot(q,type="l"); points(floor(q),col="red");
> points(floor(q)+runif(100,0,1),col="blue")
> This gives pretty good results for uniform distributions, but less
> good for others (like exponential).  Is there a better
> interpolation/smoothing function for cases like this, either Monte
> Carlo as above or deterministic?
> Thanks,
>           -s
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