How can I condition any error bar function that use the arrows() function,
such as 'CI.plot' (see example below) or 'error.bars', to draw only upper
error bar (upper CI) if the bar value (mean) is positive and the lower
error bar (lower CI) if bar value is negative?

CI.plot <- function(mean, se,length, ylim=c(-5, max(CI.H)), ...) {
    CI.H <- mean+se
    CI.L <- mean-se
    xvals <- barplot(mean, ylim=ylim, ...) # Plot bars
    arrows(xvals, mean, xvals, CI.H, angle=90,length=length)
    arrows(xvals, mean, xvals, CI.L, angle=90,length=length)
}

CI.plot(D,SE,0.01)

thanks,
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