[R] Bar plot with error bars

[Manuel Morales]

Hi Katherine,

If you have the original data, you can use the function barplot.CI from
the package sciplot which will calculate the means and CI's for you.
Examples are at: http://mutualism.williams.edu/sciplot

If you have the means and CI's already calculated, the following
function will do what you want:

CI.plot <- function(mean, std, ylim=c(0, max(CI.H)), ...) {
    CI.H <- mean+1.96*std # Calculate upper CI
    CI.L <- mean-1.96*std # Calculate lower CI
    xvals <- barplot(mean, ylim=ylim, ...) # Plot bars
    arrows(xvals, mean, xvals, CI.H, angle=90) # Draw error bars
    arrows(xvals, mean, xvals, CI.L, angle=90)
}

On Mon, 2007-10-22 at 17:03 -0400, Katherine Jones wrote:
> Apologies if this has been asked before. I am having trouble  
> understanding the R mailing list never mind R!
> 
> I am relatively new to R having migrated from Minitab nd SPSS. I  
> have managed to do some more complicated statistics such as  
> hierarchical partitioning of variance on an 80,000 record dataset but  
> have to admit that drawing a simple bar plot I could do by hand is  
> proving extremely difficult!
> 
> I have Crawley's 'The R book' which is proving  a big help, but still  
> does not provide me with all of the information I need.
> 
> What I want to do:-
> I have a small dataset, with 'rate' as the dependent variable (y axis  
> variable) and two groups ('cat' and 'box') which I have calculated  
> the mean and standard error for and would like to display as a bar  
> plot. I would like to display the standard error for each group NOT a  
> pooled standard error (i.e. error bars will be different heights on  
> the two bars). In the Crawley book, he just repeats the same error  
> bars across all groups, and I don't know how to specify the different  
> error for each bar.
> 
> What I have managed to do so far:-
> -calculate mean and standard error
> -plots means with confidence intervals
> -plot means as bar plot but with no error bars or confidence intervals
> -everything except what I want to do!
> 
> I have learnt a lot about R but it is getting rather frustrating that  
> I can do complex GLMs but cannot do a simple plot in 4 hours! I have  
> migrated to R because I like the way it can do almost anything and  
> because I'm trying to go almost completely freeware as everytime I  
> move institution I run into trouble with getting software licenses  
> which also tend to be expensive. However, I'm not the most computer  
> literate person and have grown up with 'menus' and 'windows'.
> 
> Any help much appreciated as it will save me much time and frustration!
> 
> Dr. Katherine Jones
> Department of Biology,
> Carleton University
> 
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