[R] function arguments: name of an object vs. call producing the object?

[Michael Friendly]

Thanks, Duncan

In my context, the following gives me what I want:

 > foo.glm <- function(object) {
+     if (typeof(substitute(object))=="symbol")
+     oname <- as.character(sys.call())[2]
+     else oname <- NULL
+     oname
+ }
 >
 >
 >
 > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
 > foo.glm(indep)
[1] "indep"
 >
 > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data = 
Mental))
NULL
 >


Duncan Murdoch wrote:
> On 16/03/2010 8:26 AM, Michael Friendly wrote:
>> In a function, say foo.glm for glm objects I want to use the name of 
>> the object as a label for some output,
>> but *only* if a glm object was passed as an argument, not a call to 
>> glm() producing that object.
>> How can I distinguish these two cases?
>
> Look at typeof(substitute(object)).  For example,
>
> > f <- function(object) typeof(substitute(object))
> > f(aname)
> [1] "symbol"
> > f(aname+1)
> [1] "language"
>
> That will tell you if an object was passed by name, or if you got an 
> expression to produce the object.
>
> One problem with this approach is that it only looks at the direct 
> call to f, for example
>
> > g <- function(x) f(x)
> > g(aname + 1)
> [1] "symbol"
>
> because substitute looks at the f(x) call, not the g(aname + 1) call.
>
> Duncan Murdoch
>
>
>>
>> For example, I can use the following to get the name of the argument:
>>
>> foo.glm <- function(object) {
>>     oname <- as.character(sys.call())[2]
>>     oname
>> }
>>
>>  > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
>>  > foo.glm(indep)
>> [1] "indep"
>>
>> But in foo.glm() I want to avoid using this as oname:
>>  > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data 
>> = Mental))
>> [1] "glm(formula = Freq ~ mental + ses, family = poisson, data = 
>> Mental)"
>>
>> Here is Mental, if it matters.
>>
>>  dput(Mental)
>> structure(list(ses = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
>> 2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 6L, 6L, 6L,
>> 6L), .Label = c("1", "2", "3", "4", "5", "6"), class = c("ordered",
>> "factor")), mental = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L,
>> 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L,
>> 4L), .Label = c("Well", "Mild", "Moderate", "Impaired"), class = 
>> c("ordered",
>> "factor")), Freq = c(64L, 94L, 58L, 46L, 57L, 94L, 54L, 40L,
>> 57L, 105L, 65L, 60L, 72L, 141L, 77L, 94L, 36L, 97L, 54L, 78L,
>> 21L, 71L, 54L, 71L)), .Names = c("ses", "mental", "Freq"), row.names 
>> = c(NA,
>> -24L), class = "data.frame")
>>
>


-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA