barplot x-axis labels with hierarchical grouping variables in separate rows

Question

In Excel, with data organized like so:

                                              Bare NP                   Singular-Marked NP               Plural-Marked         


        

Answer 1

A bit of manual adjustment of the margins and calling axis() twice can get you there. Saving a barplot like bp <- barplot(...) saves the midpoints of each bar for future reference.

oldpar <-par(mar=c(7,5.1,4.1,2.1))

bp <- barplot(a,
        col=c("blue","red","purple"),
        ylab="Frequency of Interpretation",
        xlab="",
        main="Frequency of BrP and AmE Interpretations \n of NPs in Neutral Environments",
        axisnames=FALSE
       )

You can then use the values stored in bp to align things properly. You can align the group and sub-group labels using the line=... argument to axis()

avgpts <- tapply(bp,rep(1:3,each=2),mean)
grps <- c("Bare NP","Singular-Marked NP","Plural-Marked NP")
subgrps <- c("BrP","AmE")
axis(1,at=bp,labels=rep(subgrps,3), cex.axis=0.7)
axis(1,at=avgpts,labels=grps, cex.axis=0.7,line=1.5,lwd=0)

title(xlab="Form of NP and Native Language",line=4.5)

Resulting in: