[R] Names of Greek letters stored as character strings; plotmath.

[Bert Gunter]

... and here is another incantation that may be  informative.

xnm<- as.name("gamma')  ## This does the parsing
plot(0, xlab =bquote(.(xnm))

The initial puzzle is that if you just set
xnm <- "gamma"

bquote will insert the string "gamma" rather than the symbol. After
all, that's what plotmath sees for xnm. So the key is telling plotmath
that it's a symbol, not a string. This can either be done before, as
above, or inline, as you and Gabor showed. Unsurprisingly. this also
does it, since as.name() is doing the parsing:

xnm <- "gamma"
 plot(0,xlab=bquote(.(as.name(xnm))))

AND we are adhering to Thomas's dictum: bquote is a wrapper for
substitute(), which is what he recommends as the preferable
alternative to eval(parse(...)) . But, heck -- all such software
principles are just guidelines. Whatever works (robustly).

HTH.

Cheers,
Bert

On Sat, May 19, 2012 at 3:17 AM, Gabor Grothendieck
<ggrothendieck at gmail.com> wrote:
> On Sat, May 19, 2012 at 1:18 AM, Rolf Turner <rolf.turner at xtra.co.nz> wrote:
>>
>> I had such good luck with my previous question to r-help, (a few minutes
>> ago) that I thought I would try again with the following query:
>>
>>> Suppose I have
>>>
>>>    xNm <- "gamma"
>>>
>>> I would like to be able to do
>>>
>>>    plot(1:10,xlab = <something involving xNm">)
>>>
>>> and get the x axis label to be the Greek letter gamma
>>> (rather than the literal text string "gamma").
>>>
>>> Is this possible?  I've messed around with substitute()
>>> and bquote() and got nowhere.
>>
>>
>> Then, just before clicking on "Send", I had one more thimk, and blow
>> me down, I got something that worked:
>>
>> plot(1:10,xlab=eval(expression(parse(text=xNm))))
>>
>
> That can be shortened to:
>
> plot(0, xlab = parse(text = xNm))
>
> --
> Statistics & Software Consulting
> GKX Group, GKX Associates Inc.
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> email: ggrothendieck at gmail.com
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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