[R] Lattice: multiple data sets on same plot

[Felix Andrews]

library(reshape)  ## the easy way
xx <- melt(x)
head(xx)

densityplot(~ value | cat1 * cat2, xx, groups = paste(variable, which),
            plot.points=FALSE, auto.key=list(columns=2),
            par.settings = simpleTheme(col = c("red","blue"), lty=c(1,1,2,2)))


Hint: using multiple terms in the formula as you did actually maps
into the "groups" argument. It is generally not a good a idea to do
that when you also specify "groups" directly.


2009/12/3 Joel Thomas <joeliol at gmail.com>:
> Hi,
> I have two data sets; one is a population and the other a sample of
> that population. I am trying to plot both on the same trellis display.
>
> # Example data set with two numerical attributes and two categorical
> pop <- data.frame(var1=rnorm(2000, 2000, 500), var2=rnorm(2000, 2000, 500))
>
> cat<-(runif(2000)<=.5)+0
> for(i in 1:length(cat)){
>   if(cat[i] == 0){
>      pop[i,"cat1"] = "this"
>   }
>   else{
>      pop[i,"cat1"] = "that"
>   }
> }
> cat<-(runif(2000)<=.5)+0
> for(i in 1:length(cat)){
>   if(cat[i] == 0){
>      pop[i,"cat2"] = "here"
>   }
>   else{
>      pop[i,"cat2"] = "there"
>   }
> }
>
> #Extract sample
> sam <- pop[sample(1:2000,50),]
>
> #Combine data sets
> x <- make.groups(pop, sam)
>
> #Create trellis display
> densityplot(~var1 + var2 | cat1 * cat2, data=x, groups=which,
> plot.points=FALSE, auto.key=list(columns=2))
>
>
> This does not produce what I want. I would like four density plots in
> each panel; var1 and var2 from the sample data as solid lines and var1
> and var2 from the population data as dotted lines with matching
> colours.
>
> densityplot(~ var1 + var2 | cat1 * cat2, data=x, groups=which,
>      panel=panel.superpose,
>      panel.groups = function(x, y,...){
>        panel.densityplot(x, ...)
>        })
>
> ... gives the same result.
>
> I've read "The panel function demystified" section of the book many
> times and still find the panel function mystifying. Could someone
> please explain how to do this and also how it works. Thankyou
>
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> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Felix Andrews / 安福立
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