[R] how to plot numeric variable against several categories with lattice bwplot?

[Rolf Turner]

On Thu, 13 Jan 2022 20:38:04 +0100
Luigi Marongiu <marongiu.luigi using gmail.com> wrote:

> Hello,
> I have a numerical variable (x) and a series of categories. I would
> like to make a box plot of x against each of the categories. How can I
> arrange the data so that I can accomplish it with lattice?
> At the moment I got this:
> ```
> df = data.frame(x = c(rep(1,5), rep(2,5), rep(3,5)),
> y = rnorm(15),
> f1 = rep(letters[1:5],3),
> f2 = rep(letters[7:9],5),
> f3 = c(rep(LETTERS[10:12],4), LETTERS[10:12]))
> df$x = factor(df$x)
> df$f1 = factor(df$f1)
> df$f2 = factor(df$f2)
> df$f3 = factor(df$f3)
> library(lattice)
> bwplot(y ~ x, data = df, auto.key = TRUE )
> ```
> Also, is it possible to have the wishers in solid line?
> Thank you

It is not at all clear to me what your are trying to do.  If you really
want "to make a box plot of x against each of the categories", you
could just do:

bwplot(x ~ f1, data = df, auto.key = TRUE )
bwplot(x ~ f2, data = df, auto.key = TRUE )
bwplot(x ~ f3, data = df, auto.key = TRUE )

successively.  But perhaps you meant "y" rather than "x".  Please
clarify what you wish to accomplish.

As to displaying the *whiskers* as solid lines ... that is one hell of
a good question!  I had to struggle:

xxx <- trellis.par.get("box.umbrella")
xxx$lty <- 1
trellis.par.set(box.umbrella=xxx)
junk <- rnorm(42)
bwplot(junk)

That gave me a boxplot "lying on its side"; I wanted one "standing up".
After a great deal more struggle I did

crud <- factor(rep(1,42),labels="")
bwplot(junk ~ crud,ylab="")

which gave me what I was after.

Perhaps others who are more knowledgeable than I could chip in with
better ideas.

But first Luigi must clarify what he wants to obtain.

cheers,

Rolf Turner

-- 
Honorary Research Fellow
Department of Statistics
University of Auckland
Phone: +64-9-373-7599 ext. 88276