[R] pairs() help - colour histograms on diagonal

[Duncan Murdoch]

Nathan S. Watson-Haigh wrote:
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> I'd like to be able to colour histograms along the diagonal using the colours
> stored in colnames(d):
>
>   
>> d
>>     
>          black        blue        brown        cyan
> 1   0.96405751 -0.02964390 -0.060147424 -0.06460070
> 2  -0.03614607  0.95475444 -0.152382053 -0.07767974
> 3  -0.07095613 -0.05884884 -0.061289399 -0.06445973
> 4  -0.03708223 -0.05997624 -0.054044275 -0.08291373
> 5  -0.08877190 -0.07193658 -0.078598617 -0.08892916
> 6  -0.09294377 -0.05563854 -0.051405213 -0.08442332
> 7  -0.08431200 -0.01657793 -0.119773022 -0.07364633
> 8  -0.06105875 -0.05311773 -0.062928495 -0.06982507
> 9  -0.05757523 -0.02589045 -0.102312333 -0.05616588
> 10 -0.05092343 -0.03935830 -0.062069716 -0.05402492
> 11 -0.08057353 -0.12690058 -0.004248301 -0.06850326
> 12 -0.08052613 -0.04962747 -0.098955086 -0.06496541
> 13 -0.07901151 -0.07587651 -0.077401999  0.96525294
> 14 -0.07187448 -0.15431262  0.952982852 -0.06471004
> 15 -0.07230232 -0.13704876  0.032573081 -0.05040565
>
>
>
> So I'd like the top-left histogram on the diagonal to be coloured black, then
> the next one on the diagonal to be coloured blue etc. Is this possible?
>
>   
Normally information about what is being plotted isn't passed to the 
panel function, and attributes of the columns are stripped off before 
passing, so this isn't easy.

If you want to do some ugly programming, you can look up the variable i 
in the sys.frame(2) environment; that will be the column number.  While 
you're at it, you might as well get the data too:  it's called x there. 
  For example,

d <- data.frame(black=rnorm(100), blue=rnorm(100), brown=rnorm(100), 
cyan=rnorm(100))

panel.hist <- function(x, ...) {
    # get some graphical parameter settings, and reset them on exit
    usr <- par("usr")
    on.exit(par(usr))
   
    par(usr = c(usr[1:2], 0, 1.5) )
   
    # get a histogram of the data, but don't plot it - we just need to 
get some info from the histogram
    h <- hist(x, plot = FALSE)
    breaks <- h$breaks
    nB <- length(breaks)
    y <- h$counts; y <- y/max(y)

    colnum <- parent.frame(2)$i    
    x <- parent.frame(2)$x
    colour <- colnames(x)[colnum] 
   
    rect(breaks[-nB], 0, breaks[-1], y, col=colour, ...)
}

pairs(d, upper.panel=panel.smooth, diag.panel=panel.hist)

Duncan Murdoch

> Cheers,
> Nathan
>
> - --
> - --------------------------------------------------------
> Dr. Nathan S. Watson-Haigh
> OCE Post Doctoral Fellow
> CSIRO Livestock Industries
> Queensland Bioscience Precinct
> St Lucia, QLD 4067
> Australia
>
> Tel: +61 (0)7 3214 2922
> Fax: +61 (0)7 3214 2900
> Web: http://www.csiro.au/people/Nathan.Watson-Haigh.html
> - --------------------------------------------------------
>
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