R help - Jun 2013 - Superpose two QQ-plots (gamma distribution) with lattice function qqmath()

Hello,

I am trying to superpose on a single panel two QQ plots with the lattice 
qqmath function.

Here is a reproducible example of the problem I am facing:

# Generate data
shape = 8
rate = c(rep(1/4,100),rep(1/3,100))
x = rgamma(200,shape,rate)
groups = gl(2,100,200,labels=LETTERS[1:2])

# Plot
qqmath(~x,groups=groups,panel = "panel.superpose",
distribution = function(x) qgamma(x,shape,rate),
panel.groups = function(x,subscripts,...) {
	panel.qqmath(x,shape=shape,rate=rate[subscripts],...)
	panel.qqmathline(x,shape=shape,rate=rate[subscripts],...)
})

Both data series seem to be reproduced twice, somewhat rescaled.

I don't understand what this mean.

What am I doing wrong?

Thanks a lot for your help,

Yvonnick Noel
University of Brittany, Rennes
Dpt. of Psychology
France

Your "rate" variable is not a single value, but a vector of 200!.
I'm surprised you get anything at all. You have to pick one rate
value to use to create the values for the x-axis. For example run
> rate <- 1/4
And then run the qqmath() function.

Or, change the rate variable in the ggamma() function to

qgamma(x,shape,1/4).

-------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77840-4352

-----Original Message-----
From: r-help-bounces at r-project.org
[mailto:r-help-bounces at r-project.org] On Behalf Of Yvonnick Noel
Sent: Friday, June 21, 2013 9:55 AM
To: r-help at r-project.org
Cc: Deepayan.Sarkar at r-project.org
Subject: [R] Superpose two QQ-plots (gamma distribution) with
lattice function qqmath()

Hello,

I am trying to superpose on a single panel two QQ plots with the
lattice 
qqmath function.

Here is a reproducible example of the problem I am facing:

# Generate data
shape = 8
rate = c(rep(1/4,100),rep(1/3,100))
x = rgamma(200,shape,rate)
groups = gl(2,100,200,labels=LETTERS[1:2])

# Plot
qqmath(~x,groups=groups,panel = "panel.superpose",
distribution = function(x) qgamma(x,shape,rate),
panel.groups = function(x,subscripts,...) {
	panel.qqmath(x,shape=shape,rate=rate[subscripts],...)
	panel.qqmathline(x,shape=shape,rate=rate[subscripts],...)
})

Both data series seem to be reproduced twice, somewhat rescaled.

I don't understand what this mean.

What am I doing wrong?

Thanks a lot for your help,

Yvonnick Noel
University of Brittany, Rennes
Dpt. of Psychology
France

______________________________________________
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https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

Hi

Following on David's rate argument

try (with modifications of pch and grid)

rate <- 1/4
shape = 8
rate = c(rep(1/4,100),rep(1/3,100))
x = rgamma(200,shape,rate)
groups = gl(2,100,200,labels=LETTERS[1:2])
dat = data.frame(x=x, gp=groups)

qqmath(~ x,  data = dat,
        groups = gp,
        pch = 20,
        type = c("p","g"),
        distribution = function(x) qgamma(x,shape,rate),
        panel = function(x,groups,...) {
                  panel.qqmath(x,groups, ...)
        })

Duncan

Duncan Mackay
Department of Agronomy and Soil Science
University of New England
Armidale NSW 2351
Email: home: mackay at northnet.com.au


At 00:55 22/06/2013, you wrote:
>Hello,
>
>I am trying to superpose on a single panel two QQ plots with the 
>lattice qqmath function.
>
>Here is a reproducible example of the problem I am facing:
>
># Generate data
>shape = 8
>rate = c(rep(1/4,100),rep(1/3,100))
>x = rgamma(200,shape,rate)
>groups = gl(2,100,200,labels=LETTERS[1:2])
>
># Plot
>qqmath(~x,groups=groups,panel = "panel.superpose",
>distribution = function(x) qgamma(x,shape,rate),
>panel.groups = function(x,subscripts,...) {
>         panel.qqmath(x,shape=shape,rate=rate[subscripts],...)
>         panel.qqmathline(x,shape=shape,rate=rate[subscripts],...)
>})
>
>Both data series seem to be reproduced twice, somewhat rescaled.
>
>I don't understand what this mean.
>
>What am I doing wrong?
>
>Thanks a lot for your help,
>
>Yvonnick Noel
>University of Brittany, Rennes
>Dpt. of Psychology
>France
>
>______________________________________________
>R-help at r-project.org mailing list
>https://stat.ethz.ch/mailman/listinfo/r-help
>PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>and provide commented, minimal, self-contained, reproducible code.
>