Thanks, Bill & Duncan. Actually I tried values which are inside the defined
region. please find below the extracted script

> xnew<-rlnorm(seq(0,4000000,10000), meanlog=9.7280055, sdlog=2.0443945)
> f <- ecdf(xnew)
> y <- f(x)
> y1<-f(2000000)                ## finding y for a given xnew value of
2000000
> y1
[1] 0.9950125                    ## It works.

> inv_ecdf <- function(f){
+ xnew <- environment(f)$xnew
+ y <- environment(f)$y
+ approxfun(y, xnew)
+ }
## Interpolation to find xnew for a known y value.

> g <- inv_ecdf(f)
> g(0.9950125)
[1] NA
> g(0.99)  ## It doesn't
[1] NA
> g(0.5)
[1] NA     ## again
> g(0.2)
[1] NA     ## and again


I am stuck here. Any help is appreciated.

Mano.


On Fri, Nov 1, 2013 at 2:48 AM, William Dunlap <wdunlap@tibco.com> wrote:

> > it gives 'NA' (for whatever y value).
>
> What 'y' values were you using?  inf_f maps probabilities (in [0,1]) to
> values in the range of the orginal data, x, but it will have problems for
> a probability below 1/length(x) because the original data didn't tell
> you anything about the ecdf in that region.
>
>    > X <- c(101, 103, 107, 111)
>    > f <- ecdf(X)
>    > inv_f <- inv_ecdf(f)
>    > inv_f(seq(0, 1, by=1/8))
>    [1]  NA  NA 101 102 103 105 107 109 111
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com
>
>
> > -----Original Message-----
> > From: r-help-bounces@r-project.org [mailto:r-help-bounces@r-project.org]
> On Behalf
> > Of Manoranjan Muthusamy
> > Sent: Thursday, October 31, 2013 6:18 PM
> > To: Rui Barradas
> > Cc: r-help@r-project.org
> > Subject: Re: [R] Extracting values from a ecdf (empirical cumulative
> distribution function)
> > curve
> >
> > Thank you, Barradas. It works when finding y, but when I tried to find x
> > using interpolation for a known y it gives 'NA' (for whatever y value). I
> > couldn't find out the reason. Any help is really appreciated.
> >
> > Thanks,
> > Mano
> >
> >
> > On Thu, Oct 31, 2013 at 10:53 PM, Rui Barradas <ruipbarradas@sapo.pt>
> wrote:
> >
> > > Hello,
> > >
> > > As for the problem of finding y given the ecdf and x, it's very easy,
> just
> > > use the ecdf:
> > >
> > > f <- ecdf(rnorm(100))
> > >
> > > x <- rnorm(10)
> > > y <- f(x)
> > >
> > > If you want to get the x corresponding to given y, use linear
> > > interpolation.
> > >
> > > inv_ecdf <- function(f){
> > >         x <- environment(f)$x
> > >         y <- environment(f)$y
> > >         approxfun(y, x)
> > > }
> > >
> > > g <- inv_ecdf(f)
> > > g(0.5)
> > >
> > >
> > > Hope this helps,
> > >
> > > Rui Barradas
> > >
> > > Em 31-10-2013 12:25, Manoranjan Muthusamy escreveu:
> > >
> > >> Hi R users,
> > >>
> > >> I am a new user, still learning basics of R. Is there anyway to
> extract y
> > >> (or x) value for a known x (or y) value from ecdf (empirical
> cumulative
> > >> distribution function) curve?
> > >>
> > >> Thanks in advance.
> > >> Mano.
> > >>
> > >>         [[alternative HTML version deleted]]
> > >>
> > >> ______________________________**________________
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> > >> https://stat.ethz.ch/mailman/**listinfo/r-
> > help<https://stat.ethz.ch/mailman/listinfo/r-help>
> > >> PLEASE do read the posting guide http://www.R-project.org/**
> > >> posting-guide.html <http://www.R-project.org/posting-guide.html>
> > >> and provide commented, minimal, self-contained, reproducible code.
> > >>
> > >>
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
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> > https://stat.ethz.ch/mailman/listinfo/r-help
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> http://www.R-project.org/posting-guide.html
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>

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