Re: [R] barplot as Trellis graphic

From: Charilaos Skiadas <cskiadas_at_gmail.com>
Date: Fri, 28 Mar 2008 07:49:00 -0400

On Mar 28, 2008, at 2:42 AM, Agustin Lobo wrote:

> 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!

Perhaps this:

datos5 <- with(datos4,aggregate(rep(1,nrow(datos4)), list (V1=V1,SITE=SITE),sum))
barchart(x~ordered(V1)|SITE, data=datos5)

> Is there an R guide to Trellis graphics?

I found Paul Murrell's book useful.

> Agus

Haris Skiadas
Department of Mathematics and Computer Science Hanover College

> 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



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