R help - Apr 2004 - percentile-percentile plot

Hi,

Is there a function that does percentile-percentile plot. I do not mean
the qqplot. I need to plot the percentiles rather than points themselves.
I am hoping for a plot that tells me that the x percentile of one data set
corresponds to the y percentile of the other. for example a point on the
plot of (.5, .2) will tell me that the 50th percentile of the first data
and the 20th percentile of the second data are equal.

Is there any function that does this?
Thank you for the help,
Jean,

On 6 Apr 2004 at 13:33, Jean Eid wrote:

qqplot(x,y)

Kjetil Halvorsen
> 
> Hi,
> 
> Is there a function that does percentile-percentile plot. I do not
> mean the qqplot. I need to plot the percentiles rather than points
> themselves. I am hoping for a plot that tells me that the x percentile
> of one data set corresponds to the y percentile of the other. for
> example a point on the plot of (.5, .2) will tell me that the 50th
> percentile of the first data and the 20th percentile of the second
> data are equal.
> 
> Is there any function that does this?
> Thank you for the help,
> Jean,
> 
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On Tue, 6 Apr 2004 13:33:58 -0400, Jean Eid
<jeaneid at chass.utoronto.ca> wrote :
>Hi,
>
>Is there a function that does percentile-percentile plot. I do not mean
>the qqplot. I need to plot the percentiles rather than points themselves.
>I am hoping for a plot that tells me that the x percentile of one data set
>corresponds to the y percentile of the other. for example a point on the
>plot of (.5, .2) will tell me that the 50th percentile of the first data
>and the 20th percentile of the second data are equal.
>
>Is there any function that does this?
I think you'll have to write your own.  Here's a rough start:

ppplot <- function(x,y) {
  x <- sort(x)
  y <- sort(y)
  px <- ppoints(x)
  py <- ppoints(y)
  plot(px, approx(y, py, x)$y)
}

This function messes up if the distributions are too different; you'll
need to fix up the approx call somehow.

Duncan Murdoch