custom width of bars about lattice-tools HOT 1 CLOSED

# alternatively, means and error margins can be supplied directly. 
# In this case means are supplied as unique combinations
# of y and x while error_margin is a separate vector with same length as y.
mtcars_means <- data.frame(
  cyl = sort(unique(mtcars$cyl)),
  mpg = with(mtcars, tapply(mpg, cyl, mean)),
  stdev = with(mtcars, tapply(mpg, cyl, sd))
)

# you might have to adjust the yscale as it is determined from the
# range of the y variable only, ignoring the extension through error bars.
xyplot(mpg ~ factor(cyl), mtcars_means,
  error_margin = mtcars_means$stdev,
  ylim = c(9, 36), groups = cyl,
  lwd = 2, pch = 19, cex = 1.5,
  panel = function(x, y, ...) {
    panel.errbars(x, y, ...)
  }
)