[R] Bar plot with error bars

Katherine Jones kajones at connect.carleton.ca
Mon Oct 22 23:03:41 CEST 2007

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 and 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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