[R] offlist Re: Svy function doesn't work nested in user-defined function

[David Winsemius]

On May 21, 2010, at 11:48 AM, Thomas Lumley wrote:

> On Thu, 20 May 2010, David Winsemius wrote:
>
>> Almost. Testing with the examples on svytable help page:
>>
>> test <- function(Z){ 			
>>  fmla <- as.formula( paste(" ~ ", paste(c(Z, "stype"), collapse=  
>> "+")))
>>  chisq <- svychisq( fmla, design=rclus1,
>>                                statistic="adjWald", round=4)
>> }
>>
>> reslt <- test("sch.wide")
>> reslt
>>
>> 	Design-based Wald test of association
>>
>> data:  svychisq(fmla, design = rclus1, statistic = "adjWald", round  
>> = 4)
>> F = 2.2296, ndf = 2, ddf = 13, p-value = 0.1471
>>
>> The "con" object probably does not exist, so one needs to pass a  
>> character name to the formula.
>>
>
> That works, but you can see why I prefer
>
> test<-function(formula){
>    svychisq(update(formula, ~.+stype), dclus1)
> }
>
> test(~sch.wide)
>

I certainly can see the reason for your preference. Much cleaner. I  
also looked at the help page for update.formula as suggested by the  
update help page. So, when the R interpreter encounters the "~" in the  
test call, it acts in a manner something akin to encountering back- 
quote or "$" and defers evaluation of "sch.wide"?


> Model formulas were invented for precisely this purpose. You can  
> work around them using character strings or using bare symbol names  
> and substitute, but it's really easier just to work with the formula.
>
>    -thomas
>
> Thomas Lumley			Assoc. Professor, Biostatistics
> tlumley at u.washington.edu	University of Washington, Seattle
>

David Winsemius, MD
West Hartford, CT