Phylogenetic PCA 'biplot' with choices argument

A phytools user recently asked the following:

“I am trying to plot the results of a phylogenetic PCA generated with your package Phytools. I would especially like to plot the third and fourth components using the "choices” option of the biplot() function in R. My feeling is that this option is not implemented while using your phyl.pca function since I get the message "choices" is not a graphical parameter. Am I right? Is there a way I can plot other components than the default ones?“

In fact, this is correct. Here is the function code for biplot.phyl.pca (originally suggested to me by Joan Maspons):

library(phytools)
biplot.phyl.pca

## function (x, ...) 
## {
##     biplot(x$S, x$L, ...)
## }
## <environment: namespace:phytools>

tree<-pbtree(n=26,tip.label=LETTERS)
X<-fastBM(tree,nsim=4)
obj<-phyl.pca(tree,X)
obj

## Phylogenetic pca
## Starndard deviations:
##       PC1       PC2       PC3       PC4 
## 1.0959134 0.9057384 0.8286637 0.6021671 
## Loads:
##              PC1        PC2        PC3          PC4
## [1,]  0.45746491  0.3875983  0.2376398 -0.764212515
## [2,] -0.05002709  0.3353159 -0.9366821 -0.087676734
## [3,] -0.68744007 -0.6538311 -0.1233330 -0.291066912
## [4,] -0.81927353  0.5421294  0.1867339  0.004131128

biplot(obj)

biplot(obj,choices=c(3,4)) ## doesn't work

## Warning in plot.window(...): "choices" is not a graphical parameter

## Warning in plot.xy(xy, type, ...): "choices" is not a graphical parameter

## Warning in axis(side = side, at = at, labels = labels, ...): "choices" is
## not a graphical parameter

## Warning in axis(side = side, at = at, labels = labels, ...): "choices" is
## not a graphical parameter

## Warning in box(...): "choices" is not a graphical parameter

## Warning in title(...): "choices" is not a graphical parameter

## Warning in text.default(x, xlabs, cex = cex[1L], col = col[1L], ...):
## "choices" is not a graphical parameter

## Warning in plot.window(...): "choices" is not a graphical parameter

## Warning in plot.xy(xy, type, ...): "choices" is not a graphical parameter

## Warning in title(...): "choices" is not a graphical parameter

## Warning in axis(3, col = col[2L], ...): "choices" is not a graphical
## parameter

## Warning in axis(4, col = col[2L], ...): "choices" is not a graphical
## parameter

## Warning in text.default(y, labels = ylabs, cex = cex[2L], col = col[2L], :
## "choices" is not a graphical parameter

It is non-trivial, but fairly straightforward, to modify this to permit use of the argument choices to select PC axes to be plotted. For this I made use of the do.call function:

biplot.phyl.pca<-function(x,...){
    to.do<-list(...)
    if(hasArg(choices)){ 
        choices<-list(...)$choices
        to.do$choices<-NULL
    } else choices<-c(1,2)
    to.do$x<-x$S[,choices]
    to.do$y<-x$L[,choices]
    do.call(biplot,to.do)
}

Let's try it:

biplot(obj) ## standard biplot

biplot(obj,choices=c(3,4))

That's it. Assuming I don't find (and no one points out) an error in this, I will add this to the next version of phytools.