[R] Format of numbers in plotmath expressions.

Rolf Turner rolf.turner at xtra.co.nz
Sat Oct 6 02:01:49 CEST 2012

```
Thanks Uwe.  I think your recipe is substantially sexier than mine.

However I will, I believe, ***NEVER*** understand how to put together
plotmath constructs.  They seem to require some subset of:

* expression()
* bquote()
* substitute()
* parse()
* paste()
* as.expression()
* .(...)

(and quite possibly other things that I have forgotten) in a bewildering
variety of combinations with no perceptible rationale as what combination
is required in what circumstances.

It makes quantum mechanics look simple by comparison.

cheers,

Rolf

On 06/10/12 06:58, Uwe Ligges wrote:
>
>
> On 05.10.2012 09:30, Rolf Turner wrote:
>>
>> I want to do something like:
>>
>> TH <- sprintf("%1.1f",c(0.3,0.5,0.7,0.9,1))
>> plot(1:10)
>> legend("bottomright",pch=1:5,legend=parse(text=paste("theta ==",TH)))
>>
>> Notice that the final "1" comes out in the legend as just plain "1"
>> and NOT
>> as "1.0" although TH is
>>
>> [1] "0.3" "0.5" "0.7" "0.9" "1.0"
>>
>> I can get plotmath to preserve "1.0" as "1.0" and NOT convert it to "1"
>> if I use substitute, as in
>>
>> text(2,5,labels=substitute(list(theta == a),list(a=TH[5])))
>>
>> but substitute doesn't work appropriately with vectors.
>>
>> Can anyone tell me how to get a "1.0" rather than "1" in the legend?
>>
>> Ta.
>>
>>      cheers,
>>
>>          Rolf Turner
>>
>> P.S. Just figured out a way using sapply():
>>
>> leg <- sapply(TH,function(x){substitute(list(theta == a),list(a=x))})
>> plot(1:10)
>> legend("bottomright",pch=1:5,legend=parse(text=leg))
>>
>> Note that the use of "parse" (pace Thomas Lumley! :-) ) is required ---
>> "legend=leg" does NOT work.
>>
>> Getting here required an enormous amount of trial and error. And it
>> seems
>> pretty kludgy.
>>
>> Is there a sexier way?
>
>
> Not sure what is sexier here. I'd stay with
>
> leg <- lapply(TH, function(x) bquote(list(theta == .(x))))
> plot(1:10)
> legend("bottomright", pch=1:5, legend=as.expression(leg))
>
>
> Best,
> Uwe Ligges
>
>
>
>>
>>          R. T.
>>
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