[R] Pass character vector to function argument

[David Winsemius]

On Nov 16, 2010, at 1:04 PM, Kevin Ummel wrote:

> Sorry, I shouldn't have used 'sum' as an example; I am looking for a  
> solution in the case of functions that do not result in simple  
> vectors or matrices.
>
> The "real-world" example is something like the following using the  
> 'raster' package, though (I think) any command producing an S4  
> object could be a candidate:
>
> r1 <- raster(system.file("external/test.grd", package="raster"))*1
> r2 <- raster(system.file("external/test.grd", package="raster"))*2
>
> obs=objects(pattern=glob2rx("r?"))
>
> #Would like to generate the equivalent of...
>
> stack(r1,r2)

Have you tried what would seem to be the obvious generalization of the  
example offered:

str(stack(sapply(obs, get)))   # it does not throw any error and seems  
to have data in it

>
> ...using a variation of obs as an argument to 'stack' (potentially  
> very long).

Also tested:

str(
stack( c(sapply(obs, get),sapply(obs, get)) )  # doing a four object  
test
)  # no error

(I did not see any indication in the help page for get that it's  
operation was restricted to S3 objects. If there is such a restriction  
then warnings should be added there.)


>
> Cheers,
> Kevin
>
>
> On Nov 16, 2010, at 5:07 PM, David Winsemius wrote:
>
>>
>> On Nov 16, 2010, at 10:34 AM, Kevin Ummel wrote:
>>
>>> A bit embarrassed to post this seemingly trivial question, but I  
>>> can't find anything in the archive that's quite relevant:
>>>
>>> a1=1
>>> a2=2
>>>
>>> obs=objects(pattern=glob2rx("a?"))
>>>
>>> I want to utilize 'obs' as a function argument to produce  
>>> something like:
>>>
>>> sum(a1,a2)
>>>
>>
>> ?get
>>> sum(sapply(obs, get))
>> [1] 3
>>
>>
>>> Obviously, sum(obs) doesn't work, but I've tried variations of  
>>> 'eval', 'parse', 'mget', and 'noquote' without success. What am I  
>>> missing?
>>>
>>> Thanks,
>>> Kevin
>>>
>> -- 
>> David Winsemius, MD
>> West Hartford, CT
>>
>

David Winsemius, MD
West Hartford, CT