Different Starting Point (not 0) in barplot Y-Axis?

Question

I am trying to create a simple bar graph including two bars showing the average math scores of two groups of students. The averages are 363.2 and 377.4. creating bar graph i

Answer 1

Adding xpd=FALSE and re-adding the horizontal axis works, sort of:

b <- barplot(c(363.2, 377.4), beside = TRUE, 
   ylim = c(340,380), col = c("orange", "blue"),xpd=FALSE)
axis(side=1,at=b,labels=c("group 1", "group 2"))
box(bty="l")

I claim (I can't point you to a definitive reference, although Googling "bar plot zero axis" seems to come up with useful stuff; perhaps others will chime in) that it is bad practice to draw bar graphs where the vertical axis does not include zero: the argument is that the viewer will assume that bar graphs are anchored to the origin (this argument is more commonly made when explaining why R doesn't make it easy to use a logarithmic axis for barplots: see comments here, for example). Those who feel this way would say you should use points to indicate the value instead; in this case the implicit assumption of zero-anchoring does not hold as strongly.

In other words, "here's how you can do this -- but you shouldn't" ...

Answer 2

The following can be seen if you look at ?barplot:

"xpd: logical. Should bars be allowed to go outside region?"

You just need to include xpd=FALSE in your parameters for the barplot.