barplotN<-function(x, y, err.bars="ci", col="grey",
                    length=0.05,tick=F, 
                    las=2,
                    ylab=names(y), xlab = "Group",...){
x<-as.factor(x)
par(mar=c(5,5,2,2))
means<-tapply(y, x, mean)
if (err.bars=="se") int<-sqrt(tapply(y, x, var)/(tapply(y, x, length)-1))
if (err.bars=="ci") {int<-sqrt(tapply(y, x, var)/(tapply(y, x, length)-1))*qt(0.975, tapply(y, x, length)-1)}
if (err.bars!="range") {
maxs<-means+int
mins<-means-int
}
if (err.bars=="range") {
maxs<-tapply(y, x, max)
mins<-tapply(y, x, min)
}
aa<-barplot(means,
     ylim=c(min(c(mins,0)), max(maxs+1)),
     # -abs(0.1*min(mins))     +abs(0.1*max(maxs))
     xaxt='n', col=col, xlab=xlab, ylab=ylab, las=las)
axis(1, aa, labels=levels(x), xlab=NA, tick = tick)
arrows(aa, y0=mins, y1=maxs, code=3, angle=90,
       length = 0.05)
}