[R] Newbie question - struggling with boxplots

[David Winsemius]

On Aug 16, 2011, at 5:24 PM, Geoffrey Stoel wrote:

> Hopefully I will not be flamed for this on the list, but I am  
> starting out
> with R and having some trouble with combining plots.
>
> I am playing with the famous iris dataset (checking out example  
> dataset in R
> while reading through Introduction to datamining)
>
> What I would like to do is create three graphs (combined boxplots)  
> besides
> each other for each of the three species (Setosa, Versicolour and  
> Virginica)
> with each graph showing showing four boxplots Sepal.Length,  
> Sepal.Width,
> Petal.Length and Petal.Width.
>
> I can create the boxplot for the total dataset by doing the following:
>
> data(iris);
> boxplot(iris[1:4]);
>
> However I would like to have this repeated for each Species in iris 
> $Species,
> I know I can do this with:
>
> boxplot(subset(iris,Species=="setosa", select = (1:4)));
> boxplot(subset(iris,Species=="versicolor", select = (1:4)));
> boxplot(subset(iris,Species=="virginica", select = (1:4)));
>
> but I am lazy AND I want all three to be plotted besides each other  
> AND I
> don't want to manually type the Species myself.
>
> is there an easier way to do this.... probably yes...

require(lattice)
require(reshape)
iris.m <- melt(iris, id = "Species")
 > str(iris.m)
'data.frame':	600 obs. of  3 variables:
  $ Species : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1  
1 1 1 1 ...
  $ variable: Factor w/ 4 levels "Sepal.Length",..: 1 1 1 1 1 1 1 1 1  
1 ...
  $ value   : num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...

 > bwplot(value ~ variable | Species, iris.m       )

There would also be a way to send a list of Species to a function and  
do it in base graphics but that is often less economical. In this  
can,  not so bad:

 > opar <- par(mfcol=c(2,2))
 > sapply(unique(iris$Species), function(x)  
boxplot( subset(iris,Species==x, select = (1:4))) )
 > par(opar)

>
> If you want to help me out... would be deeply appreciated..
>
> Kind regards,
>
> Geoffrey
>
> (new to R and datamining)
>
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>
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David Winsemius, MD
West Hartford, CT