[R] Lattice: barchart, error bars and grouped data

[Johannes Graumann]

Hi,

How can I, given the code snippet below, draw the error bars in the center 
of each grouped bar rather than in the center of the group?

Thanks for any hints,

Joh

library(lattice)

barley[["SD"]] <- 5
barchart(
  yield ~ variety | site, 
  data = barley,
  groups=year,
  origin=0,
  lowDev=barley[["SD"]],
  highDev=barley[["SD"]],
  panel = function(
    x,
    y,
    ...,
    lowDev,
    highDev
  ){
    panel.barchart(x, y, ...)
    panel.segments(
       as.numeric(x),
       as.numeric(y) - lowDev,
       as.numeric(x),
       as.numeric(y) + highDev,
       col = 'red', lwd = 2,
       ...)
  }
)