dotplot in R with lattice: display of vertical axis and error bars

Question

I'm trying to do a dotplot with the libraries lattice and latticeExtra in R. However, no proper representation of the values on the vertical y-axis is done. Instead of choosing the actual values of the numeric variable, R plots the rank of the value. That is, there are values [375, 500, 625, 750, ..., 3000] and R plots their ranks [1,2,3,4,...23] and chooses the scale accordingly. Has someone experienced a problem like this? How can I manage the get a proper representation with ticks like (0, 500, 1000, 1500, ...) on the vertical y-scale?

Here the program code so far:

df.dose <- read.table("data.csv", sep=",", header=TRUE)
library(lattice); library(latticeExtra)

useOuterStrips(dotplot(z ~ sample.size | as.factor(effect.size)*as.factor(true.dose),
               groups=as.factor(type), data=df.dose, as.table=TRUE))

(Added from comment below): Also, can error bars be added to the graph? I thought of the following (to be added to the call), but it doesn't seem to work. Is it possible somehow?

up=z+se, lo=z-se, panel.groups=function(x,y,..., up, lo, subscripts){ 
   up <- up[subscripts]
   lo <- lo[subscripts]
   panel.segments(lo, as.numeric(y), up, as.numeric(y), ...)
}

Here's my data: https://www.dropbox.com/s/egy25cj00rhum40/data.csv

Added: here's the relevant portion of the data using expand.grid and dput:

df.dose <- expand.grid(effect.size=c(-.5, -.625, -0.75),
                       sample.size=c(40L, 60L, 80L),
                       true.dose=c(375L, 500L, 750L, 1125L),
                       type=c("dose", "categ", "FP2", "FP1"))
df.dose$z <- c(875L, 875L, 750L, 750L, 750L, 625L, 625L, 625L, 625L, 875L, 
875L, 750L, 1000L, 1000L, 1000L, 1125L, 1000L, 875L, 1000L, 1000L, 
875L, 1000L, 1000L, 875L, 1125L, 1000L, 1000L, 1250L, 1125L, 
1000L, 1250L, 1250L, 1125L, 1250L, 1000L, 1000L, 500L, 500L, 
500L, 500L, 500L, 500L, 500L, 500L, 500L, 625L, 625L, 625L, 625L, 
625L, 625L, 625L, 625L, 625L, 750L, 750L, 625L, 750L, 750L, 750L, 
750L, 750L, 750L, 875L, 875L, 750L, 750L, 875L, 875L, 875L, 875L, 
875L, 2500L, 1500L, 1125L, 2000L, 1000L, 1750L, 250L, 500L, 500L, 
1250L, 750L, 625L, 875L, 500L, 500L, 875L, 500L, 375L, 1250L, 
875L, 750L, 1000L, 625L, 625L, 875L, 500L, 500L, 1125L, 1000L, 
875L, 1125L, 875L, 625L, 1125L, 1000L, 625L, 2500L, 2125L, 2375L, 
2000L, 750L, 2625L, 250L, 625L, 250L, 875L, 875L, 500L, 625L, 
500L, 625L, 1000L, 500L, 375L, 1000L, 875L, 625L, 875L, 500L, 
500L, 875L, 500L, 500L, 1250L, 1125L, 875L, 1125L, 875L, 750L, 
1250L, 1000L, 625L)

Answer 1

You need to makez a factor: dotplot(factor(z) ~ ...

Also you probably want some jitter in the plot to prevent overlap; try adding jitter.x=TRUE or jitter.y=TRUE, or both.

Judging by your comment below and looking at the data again, I think you're plotting the dotplot the wrong way. I think you want the lines to be for the sample sizes, not for the z's. If you really want z on the vertical axis, you then need to add horizontal=TRUE. You could also swap what is on the horizontal and vertical axes.

useOuterStrips(dotplot(z ~ factor(sample.size) | 
                             as.factor(effect.size)*as.factor(true.dose),
                  groups=as.factor(type), data=df.dose,  
                  as.table=TRUE, horizontal=FALSE, jitter.x=TRUE))

To add an error bar, it's a little more complicated because you have groups within the panels, so you need to use a panel.groups function; additionally, so that the lines don't overlap, you probably want to jitter them from side to side a little, which is best done in a custom panel function.

df.dose$se <- 200
df.dose$type <- factor(df.dose$type)
df.dose$sample.size <- factor(df.dose$sample.size)

panel.groups.mydotplot <- function(x, y, subscripts, up, lo, 
                                   col=NA, col.line=NA, ...) {
  panel.points(x, y, ...)
  panel.segments(x, lo[subscripts], x, up[subscripts], col=col.line, ...)
}
panel.mydotplot <- function(x, y, subscripts, groups, ..., jitter=0.1) {
  jitter <- seq(-1,1,len=nlevels(groups))*jitter
  xx <- as.numeric(x) + jitter[as.numeric(groups[subscripts])]
  panel.dotplot(x, y, groups=groups, subscripts=subscripts, pch=NA, ...)
  panel.superpose(xx, y, groups=groups, subscripts=subscripts,  
                  panel.groups=panel.groups.mydotplot, ...)
}
pp <- dotplot(z ~ sample.size | as.factor(effect.size)*as.factor(true.dose),
              groups=type, data=df.dose, as.table=TRUE, horizontal=FALSE,
              up=df.dose$z + df.dose$se, lo=df.dose$z - df.dose$se,
              panel=panel.mydotplot, auto.key=list(space="right"))
useOuterStrips(pp)

Answer 2

I'm not sure if I understand the problem and you asked for a lattice solution but I thought it may be helpful to see this done with ggplot2:

ggplot(data=df.dose, aes(x=sample.size, y=as.factor(z), colour=type)) +
    geom_point() + facet_grid(true.dose~effect.size)

Yields:

Or we can free the scales with:

ggplot(data=df.dose, aes(x=sample.size, y=as.factor(z), colour=type)) +
    geom_point() + facet_grid(true.dose~effect.size, scales="free")

Yielding: