In Michael Crawley's "The R Book" (which I can highly recommend for teaching undergraduate statistics) the author proposes a function that adds the standard errors with the line function. The function has three arguments: The means, the standard errors, and the bar labels. For a reproducible dataset such as:

dat1 <- data.frame(income = c((2000 + 500*rnorm(10)),(2500 + 500*rnorm(10))), gender = rep(c("m","f"),c(10,10)))

with

ybar <- tapply(dat1$income, dat1$gender, mean)
se <- tapply(dat1$income, dat1$gender, sd)/10
labels <- as.character(levels(dat1$gender))

as the means, se, and labels, respectively

the function is:

error.bars<-function(yv,z,nn) {
xv<-
barplot(yv,ylim=c(0,(max(yv)+max(z))),names=nn,ylab=deparse(substitute(yv)
))
g=(max(xv)-min(xv))/50
for (i in 1:length(xv)) {
lines(c(xv[i],xv[i]),c(yv[i]+z[i],yv[i]-z[i]))
lines(c(xv[i]-g,xv[i]+g),c(yv[i]+z[i], yv[i]+z[i]))
lines(c(xv[i]-g,xv[i]+g),c(yv[i]-z[i], yv[i]-z[i]))
}}

which can be used after plotting the data:

barplot(ybar)
error.bars(ybar, se, labels)


Zeno


-----Original Message-----
From: r-sig-teaching-bounces@r-project.org on behalf of Ali Zanaty
Sent: Sat 12/11/2010 3:43 PM
To: r-sig-teaching@r-project.org
Subject: [R-sig-teaching] adding plus/minus 1 standard devaition into eachbar in cluster bar chart
 
Dear All R users:
 
I hope that this message finds all of you well.
 
Currently, I am teaching an undergraduate course in statistics. 
 
If possible, Could you please help me out how to add plus/minus 1 standard 
deviation added to each bar into R cluster bar chart.
 
You can use the following artificial data. 
 
data cat 1 cat 2
23     1      1
45     1      1
34     1      1
5      1      1
32     1      1
44     1      1
3      2      1
1      2      1
2      2      1
3      2      1
4      2      1
5      1      2
6      1      2
7      1      2
8      1      2
544    2      2
78     2      2
543    2      2
34     2      2
89     2      2
9      1      3
43     1      3
23     1      3
45     1      3
7      1      3
5      1      3
7      1      3
6      2      3
867    2      3
3      2      3
4      2      3
5      2      3
6      2      3
7      2      3
8      2      3
9      2      3
 
I need to create a bar chart for the mean of data column for each category. I 
know how to create the cluster bar chart. But I need your help with how to add 
plus/minus 1 standard deviation into each bar.
 
Thank you so much for your helps and for your attention to this matter, and I 
look forward to hearing from you.
 
 
Regards,
 
zanaty


      
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