Brett

Hi

Searching http://www.Rseek.org will return many similar results. You might find 
the following useful in terms of your question re aligning the bars:

http://users.fmg.uva.nl/rgrasman/rpages/2005/09/error-bars-in-plots.html

The discussion on this page also refers to the errbar function in the Hmisc 
package. There are other options, searching Rseek will provide many!

Basically something along the lines of the following will 'fix' your graph:

marks <- sample(4:10, size=50, replace=TRUE)
dim(marks) <- c(10,5)                       
classavg <- colMeans (marks, na.rm=FALSE, dims = 1)

thegraph <- barplot(classavg, main="Class Average for Quizzes", xlab="Quiz", 
ylab="Average", names = c("1","2","3","4","5"), ylim=c(0,12), axis.lty=1)
str(thegraph)
max <- apply (marks, 2, max)                                            
min <- apply (marks, 2, min)                                             
arrows(thegraph, min, thegraph, max, code=3, angle=90, length=0.125)          

HTH,
Jeremy

> Hey Everyone,
>
> I'm pretty new at R and wanted to try and make some graphs with dummy data
> before using it to analyze my own. I successfully made a bar graph and
> error bars, but I can't figure out how to align them properly (currently
> they are not centered on the bars and some of them aren't even close).
> Here's the
>
> code that I'm using:
> > marks <- sample(4:10, size=50, replace=TRUE)
> > dim(marks) <- c(10,5)
> > classavg <- colMeans (marks, na.rm=FALSE, dims = 1)
> > barplot(classavg, main="Class Average for Quizzes", xlab="Quiz",
> > ylab="Average", names = c("1","2","3","4","5"), ylim=c(0,12), axis.lty=1)
>
> box()
>
> > max <- apply (marks, 2, max)
> > min <- apply (marks, 2, min)
> > arrows(1:5, min, 1:5, max, code=3, angle=90, length=0.125)
>
> The error bars are simply ranges for now (I wanted to do that before I
> tried standard deviation/error). If anyone could help me align them it
> would be much appreciated!
>
> brett
---------------
Jeremy Baxter, Statistics Department, Rhodes University, South Africa.
Views expressed above, no matter how badly spelt, are my own... I think?

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