R help - Oct 2008 - panel.groups: use group.number to define colors

Dear list,


I've been trying this for a few hours and I just don't understand how  
lattice works with groups and subscripts.

Consider the following example,


> xx <- seq(1, 10, length=100)
> x <- rep(xx, 4)
> y <- c(cos(xx), sin(xx), xx, xx^2/10)
> fact <- factor(rep(c("cos", "sin", "id",
"square"), each=100))
> fact2 <- factor(rep(c("periodic", "not periodic"),
each=100))
>
> my.df <- data.frame(x=x, y=y, fact = fact, fact2 = fact2)
>
> head(my.df)
>
>
> myColors <- c(2, 4)
>
> 	xyplot(y ~ x | fact,  data = my.df, groups = fact2,
> 	      panel =  panel.superpose,
> 	      panel.groups = function(..., group.number) {
>
> 	         panel.xyplot(...)
> 			#panel.xyplot( ..., col=myColors[group.number]) # error
> 	
> 	      })

My aim is to assign a custom color to each group, but for some reason  
the col parameter is already given to panel.xyplot and I can't find  
where it gets the values from.

Many thanks,

baptiste

_____________________________

Baptiste Augui?

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag

Not exactly sure what you want to do, but ...

In your example, you do not need groups, since the color doesn't change
within the levels of the conditioning variable (fact). Hence you can use the
panel.number() function to choose the plotting color of each panel, like
this:

## .. continuing with your example 

 myColors <- rep(c(2,4),2)

 xyplot(y ~ x | fact,  data = my.df,
 	      panel =  function(...){
            panel.xyplot(...,col=myColors[panel.number()])
         }
 	  )

If you actually **need** groups (to color different subsets of the data
within a panel differently). it does get a bit more complicated.
Incidentally, note that col is already a formal argument of panel.superpose
and was therefore  picked up in the ... argument of the panel.groups
function -- that's why you got the error you did when you repeated col
explicitly in the panel.xyplot call. By default, it's values are those of
trellis.par.get("superpose.symbol") I believe. Also, group.number
appears to
be undefined in your code.

HTH

Cheers,
Bert Gunter

On Tue, Oct 7, 2008 at 8:54 AM, baptiste auguie <ba208 at exeter.ac.uk>
wrote:
> Dear list,
>
>
> I've been trying this for a few hours and I just don't understand
how
> lattice works with groups and subscripts.
>
> Consider the following example,
>
>
>
>> xx <- seq(1, 10, length=100)
>> x <- rep(xx, 4)
>> y <- c(cos(xx), sin(xx), xx, xx^2/10)
>> fact <- factor(rep(c("cos", "sin",
"id", "square"), each=100))
>> fact2 <- factor(rep(c("periodic", "not
periodic"), each=100))
>>
>> my.df <- data.frame(x=x, y=y, fact = fact, fact2 = fact2)
>>
>> head(my.df)
>>
>>
>> myColors <- c(2, 4)
>>
>>        xyplot(y ~ x | fact,  data = my.df, groups = fact2,
>>              panel =  panel.superpose,
>>              panel.groups = function(..., group.number) {
>>
>>                 panel.xyplot(...)
>>                        #panel.xyplot( ..., col=myColors[group.number])
#
>> error
>>
>>              })
>
>
> My aim is to assign a custom color to each group, but for some reason the
> col parameter is already given to panel.xyplot and I can't find where
it
> gets the values from.
It get's the values from the 'panel.superpose' function, of which
'panel.groups' is an argument. Both the documentation and source code
for 'panel.superpose' should make this clear.
>From what I understand, what you want should be as simple as (with a
small correction to your example):


xx <- seq(1, 10, length=100)
x <- rep(xx, 4)
y <- c(cos(xx), sin(xx), xx, xx^2/10)
fact <- factor(rep(c("cos", "sin", "id",
"square"), each=100))
fact2 <- factor(rep(c("periodic", "not periodic"),
each=200))
my.df <- data.frame(x=x, y=y, fact = fact, fact2 = fact2)

myColors <- c(2, 4)

xyplot(y ~ x | fact,  data = my.df, groups = fact2, col = myColors, type =
"l")


The use of 'par.settings' is not compulsory, but would help if you
needed to add a legend; e.g.,


xyplot(y ~ x | fact,  data = my.df, groups = fact2, type = "l",
       par.settings = simpleTheme(col = myColors),
       auto.key = list(lines = TRUE, points = FALSE))


If you insist on writing your own panel function, what you need is


xyplot(y ~ x | fact,  data = my.df, groups = fact2,
       panel =  panel.superpose,
       panel.groups = function(..., col.line, type, group.number) {
           panel.xyplot(..., type = "l",
                        col.line = myColors[group.number])
       })


As Bert pointed out, you are responsible for ensuring that argument
names are not repeated by capturing and overriding them.

All of this applies to your second, more complicated, example as well.
As for the order in which the groups are plotted, it is the order of
levels(fact2), which seemed to me the most obvious (or at least the
least surprising) choice. You are free to specify the order when you
create the factor; see ?factor to learn how.

-Deepayan