[R] Pass character vector to function argument

[Kevin Ummel]

On second glance, while it works for 'stack', it doesn't appear to work for 'overlay':

> overlay(sapply(obs,get))
Error in function (classes, fdef, mtable)  : 
  unable to find an inherited method for function "overlay", for signature "list", "missing"

At this point, this may be more of a 'raster' issue for the R-Sig-Geo list...

On Nov 16, 2010, at 7:09 PM, Kevin Ummel wrote:

> Thanks, David. That does, indeed, work. It didn't occur to me that a list would do the job as an argument.
> 
> Thanks for the fix!
> 
> kevin
> 
> 
> On Nov 16, 2010, at 6:58 PM, David Winsemius wrote:
> 
>> 
>> 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
>> 
>