[R] barplot as Trellis graphic

[Agustin Lobo]

Thanks for your detailed explanation.
You are right, a set of boxplots done with bwplot
is a much better graphic for this type of data:

bwplot(V1~VAR|f,data=datos2)

This was not a good example. The barplot would be suited
for counts, ie. species composition:
datos4 <- 
data.frame(V1=round(runif(200,1,5)),SITE=factor(round(runif(200,1,3))))

where I would like a barplot of table(V1) for each site:
par(mfrow=c(3,1))
barplot(table(datos4$V1[datos4$SITE==1]))
barplot(table(datos4$V1[datos4$SITE==2]))
barplot(table(datos4$V1[datos4$SITE==3]))

I'll try with barchart!

Is there an R guide to Trellis graphics?

Agus


Charilaos Skiadas escribió:
> 
> On Mar 27, 2008, at 1:47 PM, Agustin Lobo wrote:
> 
>> Thanks, it was a matter of reshaping the data matrix as I usually have
>> it, ie:
>> datos <-
>> data.frame(x=abs(round(rnorm(100,10,5))),y=abs(round(rnorm(100,2,1))),f=factor(round(runif(100,1,3)))) 
>>
>>
>> to become:
>>
>> datos2 <-
>> data.frame(V1=c(datos[,1],datos[,2]),"VAR"=c(rep("x",100),rep("y",100)),f=factor(c(datos[,3],datos[,3]))) 
>>
>>
>> and then
>> require(lattice)
>> barchart(V1~VAR|f,data=datos2)
>>
>> I get horizontal lines in the bars that I do not understand, though.
> 
> In order to understand the lines , you should ask: What does the height 
> of each bar correspond to? As you have set things up, the "x" bar in 
> panel "1" should somehow correspond to the all values:
> 
> datos2$V1[datos2$VAR=="x" & datos2$f==1]
> [1] 15 13 14  1 18 14  8 12  7 19 10  1  5 14  7  9 14  7  5 10  6 12 10 
> 11 11  7 15
> [28]  9  4 12 17 10  4  5
> 
> 
> So you should ask yourself, how you expect R to produce a single column, 
> which in some sense corresponds to just one single number, its height, 
> from these different values. My guess is that you want R to show you 
> just the mean on each group. For me this is not a barplot, but anyway. 
> What happens in the barplot you have now, I think, is this that R will 
> start by constructing a bar with height 15, then put on it a bar of 
> height 13, then on it a bar of height 14 and so on. So the lines you see 
> account for the boxes that survive:
> 
>  > x<-datos2$V1[datos2$VAR=="x" & datos2$f==1]
>  > unique(cummax(rev(x)))
> [1]  5 10 17 19
> 
> 
> I would recommend using boxplots instead of "barplots only showing the 
> means". If you really want barplots of the means, I think you can do the 
> following:
> 
> datos3 <- with(datos2, aggregate(x=V1, by=list(VAR=VAR,f=f), mean))
> barchart(x~VAR|f, datos3)
> 
> Another option would be ggplot2 I think, but I'll let someone 
> knowledgeable with that package speak up.
> 
>> Agus
>>
> 
> Haris Skiadas
> Department of Mathematics and Computer Science
> Hanover College
> 
> 
> 
> 
> 

-- 
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012
email: Agustin.Lobo at ija.csic.es
http://www.ija.csic.es/gt/obster