# [R] ltext - adding text to each panel from a matrix

Andy Bunn abunn at whrc.org
Thu Nov 10 17:19:26 CET 2005

```Hi all (really probably just Deepayan):

In the plot below I want to add text on either side of each violin plot that
indicates the number of observations that are either positive or negative.
I'm trying to do this with ltext() and I've also monkeyed about with
panel.text(). The code below is generally what I want but my calls to
ltext() are wrong and I'm not sure how to fix them. Right now they replicate
the first column of the matrices obs.pos and obs.neg for each panel. How do
I tell ltext to advance to the next column when the next panel is plotted? I
don't see how subscripts can do it, but I bet it's something along that
line...

Thanks, Andy

rm(list = ls())
set.seed(354)
# make a bimodal dataset with three groups and three treatments
foo <- c(rnorm(150,-1,0.5), rnorm(150,1,0.25))
treatment <- factor(rep(seq(1,3),100), labels = c("Treatment 1", "Treatment
2", "Treatment 3"))
group <- factor(rep(seq(1,3),100), labels = c("Group A", "Group B", "Group
C"))
group <- sample(group)
# corrupt Group A, Treatment 2 for fun.
foo[group=="Group A" & treatment=="Treatment 2"][1:8] <- rnorm(8,1,1)
dat <- data.frame(foo,treatment,group)

# set the limits for the plot, which also tells where to put the text
my.xlim <- c(-6, 6)

# make a matrix that counts the number of obs greater or less than zero
obs.pos <- tapply(dat[dat[,1] > 0,1], dat[dat[,1] > 0,-1], length)
obs.neg <- tapply(dat[dat[,1] <= 0,1], dat[dat[,1] <= 0,-1], length)
#write some coordinate data
x.obs.pos <- rep(my.xlim[2],dim(obs.pos)[2])
y.obs.pos <- 1:dim(obs.pos)[2]
x.obs.neg <- rep(my.xlim[1],dim(obs.neg)[2])
y.obs.neg <- 1:dim(obs.neg)[2]

bwplot(treatment~foo|group, data = dat,
panel=function(...) {
panel.violin(..., col = "transparent", varwidth = F)
panel.abline(v=0, lty = "dotted")
ltext(x.obs.pos, y.obs.pos, obs.pos, pos = 2)
ltext(x.obs.neg, y.obs.neg, obs.neg, pos = 4)
},
par.strip.text = list(cex = 0.8),  xlim = my.xlim)
obs.pos
obs.neg

# note that the numbers in the plot only match the matrices for Group A,
# which is the first panel. Alas.

```