John Zabroski <johnzabroski <at> gmail.com> writes: > > I am new to R. > > I want to graph group data using a "Traditional Bar Chart with Standard > Error Bar", like the kind shown here: > http://samiam.colorado.edu/~mcclella/ftep/twoGroups/twoGroupGraphs.html > > Is there a simple way to do this?
[snip] > The best clue I have so far is Rtips #5.9: > http://pj.freefaculty.org/R/Rtips.html#5.9 which is what I based my present > solution off of. > > However, I do not understand how this works. It seems like there is no > concrete way to determine the arrow drawing parameters x0 and x1 for a > barplot. Moreover, the bars seem to be "cut off". > barplot() returns the x values you need for x0 and x1. barplot(...,ylim=c(0,xbar+se)) will set the upper y limit so the bars don't get cut off. Here are three ways to create such a barplot (I will add this to the wiki once it's back on line): (n.b.: the with() command is just a shortcut to avoid having to type testdata$xbar, testdata$group, etc.) ## 1. tweaked version of what you did above testdata <- data.frame(group=c(400,200,100,50,25), xbar= c(0.36038 , 0.35927 , 0.35925 , 0.35712 , 0.35396), se = c(0.02154,0.02167,0.02341,0.01968, 0.01931)) xvals = with(testdata, barplot(xbar, names.arg=group, main="a=4.0", xlab="Group", ylab="xbar",ylim=c(0,max(xbar+se)))) with(testdata, arrows(xvals, xbar, xvals, xbar+se, length=0.4, angle=90, code=3)) ## 2. using the plotCI function from plotrix to draw the ## arrows instead library(plotrix) xvals = with(testdata, barplot(xbar, names.arg=group, main="a=4.0", xlab="Group", ylab="xbar",ylim=c(0,max(xbar+se)))) with(testdata, plotCI(xvals, xbar, liw=0,uiw=se,add=TRUE,pch=NA,gap=FALSE)) ## 3. the most automatic way, using barplot2() from the ## gplots package library(gplots) with(testdata, barplot2(xbar,names.arg=group,main="a=4.0", xlab="Group",ylab="xbar",plot.ci=TRUE, ci.u=xbar+se,ci.l=xbar)) P.S. I hope you're not hoping to infer a statistically significant difference among these groups ... cheers Ben Bolker ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
