Hi R user,
I am just wondering how I can add Standard error bar in the interaction plot. I used the following code but I don't know how i can edit this to put a started error's bar on the mean. 
Would you give me some hints? or do other packages provide the  information about plotting the SE bar for interaction.plot?

require(graphics)
with(OrchardSprays, {
  interaction.plot(treatment, rowpos, decrease)
  interaction.plot(rowpos, treatment, decrease, cex.axis = 0.8)
  ## order the rows by their mean effect
  rowpos <- factor(rowpos,
                   levels = sort.list(tapply(decrease, rowpos, mean)))
  interaction.plot(rowpos, treatment, decrease, col = 2:9, lty = 1)
})

thanks 
 		 	   		  
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