####################################################################
### Pairwise scatterplots, put histograms on diagonal, smooths lower panels,
###   correlations on the upper panels (with size proportional to magnitude)
####################################################################
panel.hist <- function(x, ...)
{
    usr <- par("usr"); on.exit(par(usr))
    par(usr = c(usr[1:2], 0, 1.5) )
    h <- hist(x, plot = FALSE)
    breaks <- h$breaks; nB <- length(breaks)
    y <- h$counts; y <- y/max(y)
    rect(breaks[-nB], 0, breaks[-1], y, col="cyan", ...)
}
panel.cor <- function(x, y, digits=2, prefix="", cex.cor)
{
    usr <- par("usr"); on.exit(par(usr))
    par(usr = c(0, 1, 0, 1))
    r <- cor(x, y)
    txt <- format(c(r, 0.123456789), digits=digits)[1]
    txt <- paste(prefix, txt, sep="")
    if(missing(cex.cor)) cex <- 0.8/strwidth(txt)
    text(0.5, 0.5, txt, cex = cex * abs(r))
}

### Apply this by issuing this to "my.df.name":
pairs(my.df.name, lower.panel=panel.smooth, upper.panel=panel.cor, 
      diag.panel=panel.hist, main="My fancy pairs plot")