[R] How to convert array dim names to expressions for plotting?

[Bert Gunter]

It is not clear to me what you mean by "expressions" in this context.
Dimension names but be character strings -- see ?dimnames, which says:

"The dimnames of a matrix or array can be NULL or a list of the same
length as dim(x). If a list, its components are either NULL or a
character vector with positive length of the appropriate dimension of
x. "

If somehow you expect plotmath type drawn objects or R expression
objects, then you are confused. If I am just misunderstanding what you
want, then I am confused.

-- Bert

On Thu, Oct 4, 2012 at 7:27 AM, Hofert  Jan Marius
<marius.hofert at math.ethz.ch> wrote:
> Hi,
>
> I would like to use the dim names of an array as labels in a plot. In the case of character labels, this is no problem. However, if I would like to pass expressions through array dim names, they only appear as character labels in the plot and are not evaluated as expressions (see the minimal example below). How can this be done?
>
> Cheers,
>
> Marius
>
>
> require(grid)
>
> tau <- c(0.25, 0.75)
> alpha <- c(0.95, 0.99, 0.999)
> a <- array(1:6, dim=c(2,3), dimnames=list(tau=tau, alpha=alpha))
>
> taulabs <- as.expression(lapply(tau, function(t) bquote(tau==.(t))))
> dimnames(a)$tau <- taulabs # does not create expressions
> dimnames(a) # => no expressions
> dimnames(a)$tau[[1]] <- taulabs[1]
> dimnames(a)$tau[[2]] <- taulabs[2]
> dimnames(a) # => now characters
>
> gl <- grid.layout(1, 2, default.units="inch", widths=c(2,2), heights=c(2,2))
> ## grid.show.layout(gl)
> pushViewport(viewport(layout=gl))
>
> pushViewport(viewport(layout.pos.row=1, layout.pos.col=1))
> grid.rect(gp=gpar(col=NA, fill="gray80"))
> grid.text(dimnames(a)[["tau"]][1], x=0.5, y=0.5)
> upViewport()
>
> pushViewport(viewport(layout.pos.row=1, layout.pos.col=2))
> grid.rect(gp=gpar(col=NA, fill="gray50"))
> grid.text(dimnames(a)[["tau"]][2], x=0.5, y=0.5)
> upViewport()
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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