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    • Example shown in Figure 3.30 in Paul Murrell's R Graphics book.
    • Also be aware of the Hmisc histbackback function, which creates back-to-back histograms.
library(Hmisc) library(Design) data(chickwts) contents(chickwts) describe(chickwts) # Want to determine no. of chicks above # the median weight chickwts <- upData(chickwts, median.weight = ifelse(weight > median(weight, na.rm = TRUE), 1, 0), levels = list(median.weight = c("Below", "Above"))) # Look at simple table of freuquencies: with(chickwts, table(feed, median.weight))

# Let's turn the table output into a back-to-back barplot # Define the data: datta <- with(chickwts, table(feed, median.weight)) # Define some parameters: xlimit <- 15 # dependent on max frequency given in table ticks <- seq(-xlimit, xlimit, 5) # where to plac the tickmarks nlines <- nlevels(chickwts$feed) # number of groups yvals <- 1:nlines # y values for the groups h <- 0.25 # height of bars # Start plotting par(mar=c(0.5, 5, 0.5, 1)) plot.new() # start a new plot frame plot.window(xlim=c(-xlimit, xlimit), ylim=c(-2.0, nlines+0.5)) lines(rep(0, 2), c(-2.0, nlines+0.5), col="grey") segments(-xlimit, yvals, xlimit, yvals, lty="dotted") rect(-datta[, "Below"], yvals-h, 0, yvals+h, col="dark grey") rect(0, yvals-h, datta[, "Above"], yvals+h, col="light grey") mtext(levels(chickwts$feed), at=yvals, adj=1, side=2, las=2) par(cex.axis=0.5, mex=0.5) axis(1, at=ticks, labels=abs(ticks), pos = 0) tw <- 1.5*strwidth("Below") rect(-tw, -1-h, 0, -1+h, col="dark grey") rect(0, -1-h, tw, -1+h, col="light grey") text(0, -1, "Below", pos=2) text(0, -1, "Above", pos=4) text(0, -1.5, "Back-to-back Barplot of Chick Weights Below/Above Median Value", adj = 0.5)
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Topic revision: r1 - 08 Nov 2006, TheresaScott
 

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