panel - Stripplot showing mean+sd [r] -

hi want plot stripplot showing mean+sd. cannot show boxplot because have less 5 values, want use mean , sd. problem cannot calculate mean , sd inside group, rather 2 means represented in both groups , and same segments.

require(lattice)  stripplot(l ~ medium, parameters,         ylab=list(expression("lag phase - h"),cex=1.5),        xlab=list("medium", cex=1.5),        auto.key=list(columns=2, rectangles=t, points=f, pch=16, at=null ),        ylim=c(-2,15),        up=parameters$l+parameters$sd.l,        lo=parameters$l-parameters$sd.l,        panel=function(x,y,up,lo,...){          xj=jitter(as.numeric(x), factor=0.5)          panel.stripplot(xj,y,pch=16 , alpha=0.5 , factor=0.2,                          cex=1.2 , ...)          panel.abline(h=0,col="black",...)          panel.arrows(x0=xj, y0=lo,                       x1=xj, y1=up,code=3,                       angle=90, length=0.05                       ,alpha=0.5)          panel.dotplot(x=x, y=tapply(y,x,mean), col="red")          panel.segments(x0=x,x1=x,y0=mean(y)-sd(y),y1=mean(y)+sd(y),col="red")        }   ) 

if condition on medium, ~l|medium rather l~medium can calculate mean , sd each level within panel function.

for example

stripplot(~sepal.length|species,iris,   panel=function(x,y,...) {      m=mean(x)      panel.stripplot(x,y,...)      panel.stripplot(m,y,pch="|",cex=2,col=2)   } ) 

otherwise can calculate mean , sd each level outside of stripplot, using by or aggregate or similar , add these plot.