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

David, Duncan,
> 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))
I don't think the problem is related to the rate argument, which can 
well be vectorized, as is the case for a number of arguments in distrib 
functions in R (note that you are redefining it as a vector above).
> 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, ...)
>          })
This works! Thank you very much (I had spent some time on that).

I now try to add a QQ-line but face a new problem. Only one line 
appears, away from the points:
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, ...)
                   panel.qqmathline(x,groups,...)
         })

Any hint?

Thanks a lot for your help,

Yvonnick

Hi

I think  the answer lies in the allocating the distribution argument 
but I do not know how. Possibly with a prepanel function

Duncan

At 21:06 22/06/2013, you wrote:
>David, Duncan,
>>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))
>
>I don't think the problem is related to the rate argument, which can 
>well be vectorized, as is the case for a number of arguments in 
>distrib functions in R (note that you are redefining it as a vector above).
>
>>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, ...)
>>          })
>
>This works! Thank you very much (I had spent some time on that).
>
>I now try to add a QQ-line but face a new problem. Only one line 
>appears, away from the points:
>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, ...)
>                   panel.qqmathline(x,groups,...)
>         })
>
>Any hint?
>
>Thanks a lot for your help,
>
>Yvonnick
>