# [R] expressions (nesting, substitution, 2-stage evaluation)

David Winsemius dwinsemius at comcast.net
Fri Feb 28 02:17:41 CET 2014

```On Feb 27, 2014, at 3:17 PM, Bert Gunter wrote:

> ?plotmath
>
> -- Bert

Daryl;;

I think what Bert was hoping you would do was read the plotmath page and figure it out on your own but that can be a bit tricky when working with expression object vectors. Here is (perhaps) a step forward:

vectorA = c( bquote("TNF-"*alpha), bquote("IFN-"*gamma) )

for(ii in vectorA)  {
plot(0:1,0:1)
title(main = ii)
}

Now as Jim Holtman is fond of saying... what problem were you (really) trying to solve?

--
David.

>
> Bert Gunter
> Genentech Nonclinical Biostatistics
> (650) 467-7374
>
> "Data is not information. Information is not knowledge. And knowledge
> is certainly not wisdom."
> H. Gilbert Welch
>
>
>
>
> On Thu, Feb 27, 2014 at 2:58 PM, Daryl Morris <darylm at uw.edu> wrote:
>> Hi,
>>
>> I have a function which generates many plots.  To keep it simple, let's say
>> I want to set the main title based on where we are in nested loops.
>>
>> So, something like
>>
>> vectorA = c("a","b","c")
>> vectorB = c("a","b","c")
>>
>> for(ii in vectorA) { for(jj in vectorB) {
>>  plot(0:1,0:1)
>>  title(main = paste(ii,jj))
>> }
>>
>> that part is easy!   The question is what if I wanted vectorA to be an
>> expression?
>>
>> I'd like to be able to set vectorA =
>> c(expression(paste("TNF-",alpha)),expression(paste("IFN-",gamma))), and have
>> the plot title show the greek letters.
>>
>> Obviously, in the for-loop I could build the expression all at once, but
>> there are lots of programmatic reasons I'd like to be able to have this
>> program structure.  Is there a solution which modifies either/both (1) the
>> setting of main in the loop (2) how I define the vector outside of the loop?
>>
>>
>> thanks, Daryl
>>
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius
Alameda, CA, USA

```

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